@article{neupane_chase_zhao_wang_he_2021, title={Optical properties of segmented Ag-Au wire at single particle level studied with a home-built micro-spectrometer}, ISSN={["2577-8196"]}, DOI={10.1002/eng2.12439}, abstractNote={Nanomaterials having hetero‐metallic junctions are being explored for sensing, catalytic, and biomedical applications. Insight into the bimetallic junction at nanoscale is important from both fundamental and application perspectives. In this study, we synthesized segmented Au–Ag wire by sequentially electroplating Au and Ag in cylindrical pores in anodic alumina membrane filters. We probed the one photon, two photon, and second harmonic signal in Au–Ag wire at single particle level by focusing laser beam to a diffraction limited spot using a home‐built sample scanning type micro‐spectrometer. When exciting the Au–Ag junctions into the mid‐UV range using two‐photon excitation, we observed two luminescence peaks at 455 and 520 nm, respectively, possibly because of the surface plasmon resonances supported by the sharp boundary and granular nanostructures on the Au–Ag interface. Interestingly, we also observed intense second harmonic generation (SHG) signal from the junction with a yield more than two orders of magnitude higher than that from the Au tips. The SHG intensity as a function of excitation wavelength showed a similar trend to the two‐photon excited luminescence emission spectrum, indicating that the SHG signal was enhanced in the presence of optical resonances. The observation of enhanced radiative properties of the bimetallic junction in the suggested that the Au–Ag wire may serve as an excellent imaging probe or single particle sensors.}, journal={ENGINEERING REPORTS}, author={Neupane, Bhanu B. and Chase, Thomas E. and Zhao, Luyang and Wang, Gufeng and He, Lin}, year={2021}, month={Jul} }
 @article{he_lou_woody_he_2019, title={Amplification-by-Polymerization in Biosensing for Human Genomic DNA Detection}, volume={4}, ISSN={["2379-3694"]}, DOI={10.1021/acssensors.9b00133}, abstractNote={A polymerization reaction was employed as a signal amplification method to realize direct visualization of gender-specific DNA extracted from human blood in a polymerase chain reaction (PCR)-free fashion. Clear distinction between X and Y chromosomes was observed by naked eyes for detector-free sensing purposes. The grown polymer films atop X and Y chromosomes were quantitatively measured by ellipsometry for thickness readings. Detection assays have been optimized for genomic DNA recognition to a maximum extent by varying the selection of the proper blocking reagents, the annealing temperature, and the annealing time. Traditional PCR and gel electrophoresis for amplicon identification were conducted in parallel for performance comparison. In the blind test for blood samples examined by the new approach, 25 out of 26 were correct and one was false negative, which was comparable to, if not better than, the PCR results. This is the first time our amplification-by-polymerization technique is being used for chromosome DNA analysis. The potential of adopting the described sensing technique without PCR was demonstrated, which could further promote the development of a portable, PCR-free DNA sensing device for point-of-need applications.}, number={4}, journal={ACS SENSORS}, author={He, Peng and Lou, Xinhui and Woody, Susan M. and He, Lin}, year={2019}, month={Apr}, pages={992–1000} }
 @article{moening_brown_he_2016, title={Matrix-enhanced nanostructure initiator mass spectrometry (ME-NIMS) for small molecule detection and imaging}, volume={8}, ISSN={["1759-9679"]}, DOI={10.1039/c6ay02753a}, abstractNote={ME-NIMS MS imaging (right): significantly enhanced sensitivity over conventional NIMS (left) in tissue imaging.}, number={46}, journal={Analytical Methods}, author={Moening, Tara N. and Brown, Victoria L. and He, Lin}, year={2016}, pages={8234–8240} }
 @article{brown_he_2015, title={Current status and future prospects of mass spectrometry imaging of small molecules}, volume={1203}, journal={Mass spectrometry imaging of small molecules}, author={Brown, V. L. and He, L.}, year={2015}, pages={1–7} }
 @article{he_2015, title={Mass spectrometry imaging of small molecules preface}, volume={1203}, journal={Mass spectrometry imaging of small molecules}, author={He, L.}, year={2015}, pages={V-} }
 @article{brown_liu_he_2015, title={Matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS) for mass spectrometry imaging of small molecules}, volume={1203}, journal={Mass spectrometry imaging of small molecules}, author={Brown, V. L. and Liu, Q. and He, L.}, year={2015}, pages={175–184} }
 @article{moening_brown_he_2015, title={Nanostructure-initiator mass spectrometry (NIMS) for molecular mapping of animal tissues}, volume={1203}, journal={Mass spectrometry imaging of small molecules}, author={Moening, T. N. and Brown, V. L. and He, L.}, year={2015}, pages={151–157} }
 @article{zheng_chase_he_2014, title={Multiplexed miRNA detection using cationic polythiophene}, volume={6}, ISSN={["1759-9679"]}, DOI={10.1039/c3ay41752b}, abstractNote={Detection of short strands of miRNA has significant biomedical and biological implications. We report here the integration of fluorescent conjugated polymers as detection moieties with metallic striped nanorods for multiplexed detection of miR-21 and miR-122 in solution. Specifically, cationic conjugated polymers were used as chemical-coupling-free signal reporters to indicate the presence of specific miRNA molecules in solution and nanorods with self-encoded striping patterns were used as multiplexing assay substrates. A competitive assay format was developed to take advantage of stronger fluorescence output from DNA/DNA duplexes than that from DNA/miRNA duplexes. Upon selection of optimal competing DNA probes, the fluorescence signal collected was inversely proportional to the concentration of target miRNA in the system. A detection limit of fmol amounts of miRNA was achieved, with a linear response spanning across a broad dynamic range. The use of inherently encoded nanorods allowed simultaneous detection of different miRNA targets with good specificity.}, number={7}, journal={ANALYTICAL METHODS}, author={Zheng, Weiming and Chase, Thomas E. and He, Lin}, year={2014}, pages={2399–2405} }
 @article{zheng_he_2014, title={Quantitative measurements of thermodynamics and kinetics of polythiophene-DNA complex formation in DNA detection}, volume={2}, ISSN={["2047-4849"]}, DOI={10.1039/c4bm00210e}, abstractNote={Cationic polythiophene derivatives have been used as unique optical probes for various biosensing applications with great success, because their optical responses are sensitive to the conformational changes from binding to single-stranded DNA (ssDNA) to binding to double-stranded DNA (dsDNA). It has long been suggested that the binding of cationic polymers to DNA has a major impact on the thermodynamics and kinetics of DNA hybridization; yet a quantitative assessment is lacking. We report here a systematic study to quantitatively measure the thermodynamic binding constants and hybridization rates of DNA duplexes in the presence/absence of cationic polythiophene. Our results show that the dissociation constant of dsDNA in the presence of polythiophene is three orders of magnitude smaller than that in the absence of polymers. The formation of the DNA/polymer triplex is also much slower than double helical DNA formation, suggesting a rate-limiting polymer-ssDNA dissociation step prior to DNA hybridization. The hybridization rate constant is further slowed down when polymer/DNA hybridization occurs on a solid surface due to steric hindrance. Having a means to quantitatively assess the DNA hybridization efficiency in the presence of cationic polymers, we were able to improve the DNA sensing performance through a combined tuning of reaction temperature and time.}, number={10}, journal={BIOMATERIALS SCIENCE}, author={Zheng, Weiming and He, Lin}, year={2014}, pages={1471–1479} }
 @article{he_tucker_gorman_he_2011, title={Chemical amplification for in-gel DNA detection}, volume={3}, ISSN={["1759-9679"]}, DOI={10.1039/c1ay05514c}, abstractNote={We report the use of reversible addition–fragmentation chain transfer (RAFT) polymerization as a highly efficient chemical amplification means to direct visualization of DNA in porous polyacrylamide gel. It is the first time that a dynamic polymer growth on the surface of soft medium is used in signal amplification for DNA detection. In the proof-of-concept experiment, a thin acrylamide gel on a glass microscope slide formed a thin layer of uniformly crosslinked network with porous structures. Oligonucleotides of different sequences were entrapped within the gel at separate spots. Hybridization of complementary DNA detection probes introduced chain transfer agents (CTAs) into the gel via preconjugation to the probes. Surface-initiated polymer growth was prompted on the gel surface and the growth of polymer brushes at the spot where DNA hybridization occurred was monitored using infrared spectroscopy and atomic force microscopy. Visible change in the texture of the porous gel occurred after polymer growth, which offered an attractive detection alternative for in-gel DNA analysis. Compared to the results from traditional ethidium bromide staining, better detection sensitivity and specificity were achieved.}, number={11}, journal={ANALYTICAL METHODS}, author={He, Peng and Tucker, Eric Z. and Gorman, Christopher B. and He, Lin}, year={2011}, month={Nov}, pages={2463–2468} }
 @article{wu_liu_he_2011, title={Polymerization-assisted signal amplification for electrochemical detection of biomarkers}, volume={136}, number={12}, journal={Analyst [London]}, author={Wu, Y. F. and Liu, S. Q. and He, L.}, year={2011}, pages={2558–2563} }
 @article{wu_liu_he_2010, title={Activators generated electron transfer for atom transfer radical polymerization for immunosensing}, volume={26}, ISSN={["1873-4235"]}, DOI={10.1016/j.bios.2010.08.041}, abstractNote={A novel and ultrasensitive immunosensing strategy based on activators generated electron transfer for atom transfer radical polymerization (AGET ATRP) in combination with flow injection chemiluminescent (CL) and electrochemical detection was proposed. The initiator-conjugated polyclone PSA antibodies (Ab2*), prepared by coupling of N-hydroxysuccinmidyl bromoisobutyrate (initiator) with polyclone PSA antibodies (Ab2), were immobilized on the substrate surface through sandwiched immunoreactions to trigger polymerization. AGET ATRP is used for local accumulation of glycidyl methacrylate (GMA) monomers. Horseradish peroxidase (HRP) was chosen as signal species for its well-characterized chemiluminescent and electrochemical behavior, strong enzyme activity, good solubility and ease in coupling. Growth of long chain polymeric materials provided excess epoxy groups for HRP coupling, which in turn significantly increased the loading of signal molecules and enhanced the chemiluminescent and electrochemical readouts. With the proposed strategy, a detection limit of 4.0 and 1.3 pg mL−1 was obtained for flow injection chemiluminescent and electrocatalytic measurements, respectively. A more than 13- and 14-fold enhancement in the chemiluminescent intensity and electrocatalytic current was achieved comparing to the traditional sandwiched immunoassays using HRP-conjugated antibody directly. The proposed method exhibited an efficient amplification performance for immunosensing. This paved a new way for ultrasensitive detection of cancer biomarkers.}, number={3}, journal={BIOSENSORS & BIOELECTRONICS}, author={Wu, Yafeng and Liu, Songqin and He, Lin}, year={2010}, month={Nov}, pages={970–975} }
 @article{zheng_he_2010, title={Distance-Dependent Fluorescence Quenching or Conjugated Polymers on Au/kg Striped Nanorods}, volume={114}, ISSN={["1932-7455"]}, DOI={10.1021/jp1070693}, abstractNote={To understand the effect of metal surface−polymer separation on fluorescent signal intensity, we describe here our initial investigation on the fluorescent behavior of conjugated polymers near metal nanorods by attenuating the thickness of SiO2 coatings as the spacer. Our preliminary results show that the amount of fluorescence of conjugated polymers quenched by Au/Ag striped nanorods exponentially decays away from the surface in the range of 0−20 nm. This distance-dependent fluorescence quenching phenomenon is consistent with that of small organic dye molecules with a similar fluorescent profile near a metal surface. Furthermore, the results confirm that it is a valid assumption that the previously proposed superquenching model for conjugated polymers in solution is applicable to the polymers attached to a solid surface. The absolute size of polymers is irrelevant in quenching studies. Similar distance-dependent quenching trends are observed for conjugated polymers placed near metal surfaces of different...}, number={41}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Zheng, Weiming and He, Lin}, year={2010}, month={Oct}, pages={17829–17835} }
 @article{zheng_he_2010, title={Multiplexed detection of protein cancer markers on Au/Ag-barcoded nanorods using fluorescent-conjugated polymers}, volume={397}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-010-3834-1}, abstractNote={Integration of fluorescent-conjugated polymers as detection moiety with metallic striped nanorods for multiplexed detection of clinically important cancer marker proteins in an immunoassay format was demonstrated in this report. Specifically, cationic conjugated polymers were introduced to protein complexes through electrostatic binding to negatively charged double-stranded DNA, which was tagged on detection antibodies prior to antigen recognition. The intense fluorescence emission of conjugated polymers resulted in highly sensitive detection of cancer marker proteins wherein an undiluted bovine serum sample as low as approximately 25 target molecules captured on each particle was detectable. Meanwhile, the use of polymer molecules as the detection probe did not obscure the optical pattern of underlying nanorods, i.e., the encoding capability of barcoded nanorods was preserved, which allowed simultaneous detection of three cancer marker proteins with good specificity.}, number={6}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Zheng, Weiming and He, Lin}, year={2010}, month={Jul}, pages={2261–2270} }
 @article{qian_he_2010, title={Polymeric macroinitiators for signal amplification in AGET ATRP-based DNA detection}, volume={150}, ISSN={["0925-4005"]}, DOI={10.1016/j.snb.2010.08.034}, abstractNote={We report here the use of polylysine (PLL) as a carrier to bring multiple polymerization reaction initiators to surface-affixed PNA/DNA duplexes for signal amplification in polymerization-based DNA detection. Two primary benefits of the described approach have been demonstrated in this report: (1) positively charged PLL as the initiator carrier binds to PNA/DNA duplexes electrostatically; thus eliminates the need for chemical modification of each individual DNA probes prior to detection and provides a universal DNA detection scheme. (2) Furthermore, each PLL molecule brings multiple polymerization reaction initiators to each hybridization event, which leads to significantly improved detection sensitivity. Systematic investigation shows the use of longer PLL (∼215 lysine residues per chain) has yielded thicker polymer films in comparison to that of a shorter PLL (∼27 lysine residues per chain). An optimal percentage of lysine moieties modified on each PLL molecule has been determined that allowed maximum polymer growth from each modified lysine group without compromising vital electrostatic binding between unmodified amino groups and negatively charged DNA. Quantitative DNA detection has been demonstrated where the detection limit has been improved for approximately 60 times compared to the previously reported value in single-initiator-tagged DNA detection.}, number={2}, journal={SENSORS AND ACTUATORS B-CHEMICAL}, author={Qian, Hong and He, Lin}, year={2010}, month={Oct}, pages={594–600} }
 @article{qian_he_2009, title={Detection of Protein Binding Using Activator Generated by Electron Transfer for Atom Transfer Radical Polymerization}, volume={81}, ISSN={["1520-6882"]}, DOI={10.1021/ac900959v}, abstractNote={A purge-free controlled living polymerization method, activator generated by electron transfer for atom transfer radical polymerization (AGET ATRP), is used to amplify the occurrence of protein binding events. Detection of ovalbumin is demonstrated where binding of femtomole protein is differentiable from the background using ellipsometry. Moreover, binding of subpicomole protein leads to visually distinguishable spots on the sensor surface within 15 min, which signifies its potential in future development of point-of-need devices.}, number={23}, journal={ANALYTICAL CHEMISTRY}, author={Qian, Hong and He, Lin}, year={2009}, month={Dec}, pages={9824–9827} }
 @article{wu_liu_he_2009, title={Electrochemical Biosensing Using Amplification-by-Polymerization}, volume={81}, ISSN={["1520-6882"]}, DOI={10.1021/ac9011254}, abstractNote={A novel signal amplification strategy for electrochemical detection of DNA and proteins based on the amplification-by-polymerization concept is described. Specifically, a controlled radical polymerization reaction is triggered after the capture of target molecules on the electrode surface. Growth of long chain polymeric materials provides numerous sites for subsequent aminoferrocene coupling, which in turn significantly enhances electrochemical signal output. Activators generated electron transfer for atom transfer radical polymerization (AGET ATRP) is used in this study for its high efficiency in polymer grafting and better tolerance toward oxygen in air. 2-Hydroxyethyl methacrylate (HEMA) and glycidyl methacrylate (GMA) are examined to provide excess hydroxyl or epoxy groups for aminoferrocene coupling. A limit of detection of 15 pM and 0.07 ng/mL is demonstrated for DNA and ovalbumin, respectively. More than 7-fold signal enhancement in ovalbumin detection has been achieved comparing to the unamplified method. In addition, a more than 5 orders of magnitude of dynamic range is achieved with a linear correlation coefficient (R(2)) of 0.997 for DNA, and a more than 3 orders of magnitude with R(2) of 0.999 for ovalbumin. Together, the results show that the coupling of amplification-by-polymerization concept with electrochemical detection offers great promises in providing a sensitive and cost-effective solution for biosensing applications.}, number={16}, journal={ANALYTICAL CHEMISTRY}, author={Wu, Yafeng and Liu, Songqin and He, Lin}, year={2009}, month={Aug}, pages={7015–7021} }
 @article{xiao_retterer_thomas_tao_he_2009, title={Impacts of Surface Morphology on Ion Desorption and Ionization in Desorption Ionization on Porous Silicon (DIOS) Mass Spectrometry}, volume={113}, ISSN={["1932-7455"]}, DOI={10.1021/jp808844f}, abstractNote={Ordered silicon nanocavity arrays were prepared with e-beam lithography to yield systematically varied pore features and porosity (4−92%). These substrates were used to investigate the effects of substrate morphology on desorption ionization on porous silicon-mass spectrometry (DIOS-MS). Five benzylpyridinium salts, 1,2-dipalmitoyl-sn-glycero-3-phosphocholine (DPPC), and angiotensin III were used as the model molecules in the study. For substrates of the same pore depth, MS results suggested that the pore size and the interpore spacing had little impact on the laser irradiation threshold required for ionization. Instead, the laser threshold was found to be highly dependent on the overall porosity for all substrates investigated—the higher the porosity the lower the threshold. Moreover, the substrates with deeper pores but of similar porosity showed significantly reduced laser thresholds. This close relationship between laser threshold and substrate morphology was attributed to the thermal confinement prop...}, number={8}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Xiao, Yongsheng and Retterer, Scott T. and Thomas, Darrell K. and Tao, Jia-Yuan and He, Lin}, year={2009}, month={Feb}, pages={3076–3083} }
 @article{zheng_he_2009, title={Label-Free, Real-Time Multiplexed DNA Detection Using Fluorescent Conjugated Polymers}, volume={131}, ISSN={["1520-5126"]}, DOI={10.1021/ja809175q}, abstractNote={A label-free, multiplexed DNA assay using fluorescent conjugated polymers as a detection probe to illustrate hybridization on metallic striped nanorods is demonstrated. Different DNA capture probes were encoded by the different reflectivities of Au and Ag stripe patterns. Successful DNA hybridization induced an optically detectable conformational change in conjugated polythiophene derivatives from forming single-stranded DNA-polymer complexes to forming double-stranded DNA-polymer ones. The results show attomole detection sensitivity and single-mutation specificity comparable to those of single-element assays but with much improved throughput.}, number={10}, journal={JOURNAL OF THE AMERICAN CHEMICAL SOCIETY}, author={Zheng, Weiming and He, Lin}, year={2009}, month={Mar}, pages={3432-+} }
 @article{liu_xiao_pagan-miranda_chiu_he_2009, title={Metabolite Imaging Using Matrix-Enhanced Surface-Assisted Laser Desorption/Ionization Mass Spectrometry (ME-SALDI-MS)}, volume={20}, ISSN={["1879-1123"]}, DOI={10.1016/j.jasms.2008.09.011}, abstractNote={We describe here the use of a hybrid ionization approach, matrix-enhanced surface-assisted laser desorption/ionization mass spectrometry (ME-SALDI-MS) in bioimaging. ME-SALDI combines the strengths of traditional matrix-assisted laser desorption/ionization (MALDI) and SALDI and enables successful MS imaging of low-mass species with improved detection sensitivity. Using 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC) as the MS standard, MS performances of MALDI, SALDI, and ME-SALDI are systematically compared. The analyte desorption and ionization mechanism in ME-SALDI is qualitatively speculated based on the observation of significantly reduced matrix background and improved survival yields of molecular ions. Improvements in detection sensitivity of low-mass species using ME-SALDI over MALDI in imaging are demonstrated with mouse heart and brain tissues.}, number={1}, journal={JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY}, author={Liu, Qiang and Xiao, Yongsheng and Pagan-Miranda, Coral and Chiu, Yu Matthew and He, Lin}, year={2009}, month={Jan}, pages={80–88} }
 @article{zheng_he_2009, title={Particle stability in polymer-assisted reverse colorimetric DNA assays}, volume={393}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-008-2536-4}, abstractNote={"Reverse" colorimetric DNA detection by the formation of core-shell particles upon DNA hybridization is described. Specifically, the assay is based on a strategy to covalently link polymer reaction initiators to suspended nanoparticles upon DNA hybridization. These initiators then prompt polymer chain growth to form a thick polymer shell outside of particles, acting as the physical barrier to keep Au particles apart. Particles without DNA hybridization aggregate, accompanied by a pronounced solution color change from red to blue. The focus of this report is to address reaction kinetics of two co-occurring processes: polymer growth and particle aggregation during the reverse colorimetric DNA assay. The results show that Cu ions used as the polymerization catalyst bind strongly to the bases in DNA molecules, resulting in crosslinking of DNA-attached gold nanoparticles and their subsequent precipitation. Both Cu-ion-assisted particle aggregation and polymer growth are found to depend strongly on Cu ion concentration, salt concentration, and reaction temperature. Under the optimized conditions, faster polymer chain growth on the surface overcomes particle aggregation and preserves particle stability via steric stabilization.}, number={4}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Zheng, Weiming and He, Lin}, year={2009}, month={Feb}, pages={1305–1313} }
 @article{qian_he_2009, title={Surface-Initiated Activators Generated by Electron Transfer for Atom Transfer Radical Polymerization in Detection of DNA Point Mutation}, volume={81}, ISSN={["1520-6882"]}, DOI={10.1021/ac900401m}, abstractNote={Amplification-by-Polymerization reportedly offers a sensitive and detector-free approach for DNA detection. However, the requirement for an oxygen-free environment when classic radical polymerization reactions are used in signal amplification significantly limits the mobility of this approach for point-of-need applications. We report here the employment of a purge-free controlled/"living" polymerization reaction, activators generated by electron transfer for atom transfer radical polymerization (AGET ATRP), to achieve signal amplification upon DNA hybridization. Its aptitude in simplifying assay procedure and shortening assay turn-around has been demonstrated in this report, which substantiates the feasibility of using Amplification-by-Polymerization for high throughput or portable screening of genetic mutations. In addition, employment of water-soluble ascorbic acid as the reducing agent has overcome the hurdles encountered by heterogeneous AGET ATRP reactions. Optimization of AGET ATRP in the presence of oligonucleotides has been conducted where tris[(2-pyridyl)methyl]amine (TPMA) was selected as the catalyst ligand for its mild reaction rate. Effective polymer growth has been achieved when the concentration of the Cu(II) catalyst was controlled at 20 mM and ascorbic acid at 18 mM. The propagation and termination reaction constants have been derived, purporting the speculated controlled growth kinetics during polymer grafting. A linear relationship between the grafted polymer film thickness and the amount of captured DNA target sequences has been established, which provides the quantification basis during DNA detection. Detection of DNA sequences with single-point mutations has been successful regardless of the mutation site.}, number={11}, journal={ANALYTICAL CHEMISTRY}, author={Qian, Hong and He, Lin}, year={2009}, month={Jun}, pages={4536–4542} }
 @article{he_he_2009, title={Synthesis of Surface-Anchored DNA-Polymer Bioconjugates Using Reversible Addition-Fragmentation Chain Transfer Polymerization}, volume={10}, ISSN={["1526-4602"]}, DOI={10.1021/bm9002283}, abstractNote={We report here an approach to grafting DNA-polymer bioconjugates on a planar solid support using reversible addition-fragmentation chain transfer (RAFT) polymerization. In particular, a trithiocarbonate compound as the RAFT chain transfer agent (CTA) is attached to the distal point of a surface-immobilized oligonucleotide. Initiation of RAFT polymerization leads to controlled growth of polymers atop DNA molecules on the surface. Growth kinetics of poly(monomethoxy-capped oligo(ethylene glycol) methacrylate) atop DNA molecules is investigated by monitoring the change of polymer film thickness as a function of reaction time. The reaction conditions, including the polymerization temperature, the initiator concentration, the CTA surface density, and the selection of monomers, are varied to examine their impacts on the grafting efficiency of DNA-polymer conjugates. Comparing to polymer growth atop small molecules, the experimental results suggest that DNA molecules significantly accelerate polymer growth, which is speculated as a result of the presence of highly charged DNA backbones and purine/pyrimidine moieties surrounding the reaction sites.}, number={7}, journal={BIOMACROMOLECULES}, author={He, Peng and He, Lin}, year={2009}, month={Jul}, pages={1804–1809} }
 @article{liu_peng_yang_wu_he_2008, title={Electrochemistry of cytochrome P450 enzyme on nanoparticle-containing membrane-coated electrode and its applications for drug sensing}, volume={375}, ISSN={["1096-0309"]}, DOI={10.1016/j.ab.2007.12.001}, abstractNote={In the current study, we describe an improved system to study the two-electron delivery reaction pathway of cytochrome P450, family 2, subfamily B, polypeptide 6 (CYP2B6) in vitro. In particular, a biocompatible film containing colloidal gold nanoparticles and chitosan was used to encapsulate CYP2B6 on an electrode. The electrocatalytic behaviors of CYP2B6 toward common drugs in the absence of NADHP–cytochrome P450 reductase as electron donor were studied. In an anaerobic solution, direct and reversible electron transfer between the electroactive heme center of CYP2B6 and the electrode was observed with a formal potential of –0.454 ± 0.006 V at pH 7.4. In an air-saturated solution, an increase in the bioelectrocatalytic reduction current was observed after drug addition. The bioelectrocatalytic products were analyzed using high-performance liquid chromatography (HPLC) and electrospray ionization–mass spectrometry (ESI–MS). Both results confirmed that C-hydroxylation and heteroatom release were the main pathways for CYP2B6-mediated drug oxidation, similar to what occurred in vivo. The use of immobilized proteins in nanoparticle-containing films in drug biosensing was also demonstrated.}, number={2}, journal={ANALYTICAL BIOCHEMISTRY}, author={Liu, Songqin and Peng, Lei and Yang, Xiaodi and Wu, Yafeng and He, Lin}, year={2008}, month={Apr}, pages={209–216} }
 @article{wu_zhuang_liu_he_2008, title={Phenylboronic acid immunoaffinity reactor coupled with flow injection chemiluminescence for determination of alpha-fetoprotein}, volume={630}, ISSN={["1873-4324"]}, DOI={10.1016/j.aca.2008.10.010}, abstractNote={A reusable and sensitive immunoassay based on phenylboronic acid immunoaffinity reactor in combination with flow injection chemiluminescence (CL) for determination of glycoprotein was described. The reactor was fabricated by immobilizing 3-aminophenylboronic acid (APBA) on glass microbeads with γ-glycidoxypropyltrimethoxysilane (GPMS) as linkage. The α-fetoprotein (AFP) could be easily immobilized on the APBA coated beads through sugar–boronic interaction. After an off-line incubation, the mixture of the analyte AFP with horseradish peroxidase-labeled AFP antibody (HRP-anti-AFP) was injected into the reactor. This led the trapping of free HRP-anti-AFP by the surface coated AFP on glass beads. The trapped HRP-anti-AFP was detected by chemiluminescence due to its sensitizing effect on the reaction of luminol and hydrogen peroxide. Under optimal conditions, the chemiluminescent signal was proportional to AFP concentration in the range of 10–100 ng mL−1. The whole assay process including regeneration of the reactor could be completed within 31 min. The proposed system showed acceptable detection and fabrication reproducibility, and the results obtained with the present method were in acceptable agreement with those from parallel single-analyte test of practical clinical sera. The described method enabled a low-cost, time saving and was potential to detect the serum AFP level in clinical diagnosis.}, number={2}, journal={ANALYTICA CHIMICA ACTA}, author={Wu, Yafeng and Zhuang, Yafeng and Liu, Songqin and He, Lin}, year={2008}, month={Dec}, pages={186–193} }
 @article{liu_zhang_wu_tu_he_2008, title={Prostate-specific antigen detection by using a reusable amperometric immunosensor based on reversible binding and leasing of HRP-anti-PSA from phenylboronic acid modified electrode}, volume={395}, ISSN={["1873-3492"]}, DOI={10.1016/j.cca.2008.04.031}, abstractNote={In recent years, many automated immunoassay analyzers have been developed for accurate diagnosis of various disease states and to improve effective drug administration. Amperometric immunoassay has been increasingly applied to laboratory medicine due to its ease in automation, rapid speed and low detection limits. It is important to develop reusable immunologically-sensitive elements for prostate-specific antigen (PSA) detection. The strategy for the immunosensor construction is based on the enzyme-conjugated prostate-specific antibody (HRP-anti-PSA) reversible binding with a self-assembled phenylboronic acid monolayer on gold. After incubating an HRP-anti-PSA modified electrode in a PSA solution, a decrease in the electrocatalytic response of the HRP-anti-PSA modified electrode to the reduction of H2O2 is observed. The photometric activity assays show that this decrease of the electrocatalytic response arises from the formation of immunocomplexes of HRP-conjugated anti-PSA and its antigen, not from the loss of bound HRP-anti-PSA from the electrode surface. Analytical performances and optimal conditions of the described immunosensor are also investigated. Under the optimal conditions, the amperometric immunosensor shows a linear increase of the relative intensity in 2 PSA concentration range from 2 to 15 ng/ml and 15 to 120 ng/ml, respectively. This method could be used for rapid analysis of PSA and potentially other antigens.}, number={1-2}, journal={CLINICA CHIMICA ACTA}, author={Liu, Songqin and Zhang, Xiaoting and Wu, Yafeng and Tu, Yifeng and He, Lin}, year={2008}, month={Sep}, pages={51–56} }
 @article{liu_he_2008, title={Quantitative study of solvent and surface effects on analyte ionization in desorption ionization on silicon (DIOS) mass spectrometry}, volume={19}, ISSN={["1044-0305"]}, DOI={10.1016/j.jasms.2007.10.002}, abstractNote={Deuterated solvents and DIOS surfaces derivatized with different functional groups are used to investigate impacts of local chemical environment on analyte ionization. Both solvent molecules and surface functional groups are found to directly participate in analyte protonation in the condensed phase. The corresponding protonation effectiveness is quantitatively estimated based on the relative MS peak intensities of [M+2]+/[M+1]+. A direct correlation between ionization of triethylamine and the relative acidities of the surface and the solvent is evident. In addition, the proton donating effectiveness of a solvent is found to be related to its vapor pressure. Improved MS detection of small molecules via proper surface treatment and solvent selection is demonstrated.}, number={1}, journal={JOURNAL OF THE AMERICAN SOCIETY FOR MASS SPECTROMETRY}, author={Liu, Qiang and He, Lin}, year={2008}, month={Jan}, pages={8–13} }
 @article{he_zheng_tucker_gorman_he_2008, title={Reversible addition-fragmentation chain transfer polymerization in DNA biosensing}, volume={80}, ISSN={["0003-2700"]}, DOI={10.1021/ac702608k}, abstractNote={Reversible addition-fragmentation chain transfer polymerization is employed here to allow detector-free visualization of specific DNA sequences for which dynamic polymer growth is used in signal amplification. In particular, surface-initiated polymer growth was regulated by the immobilization of chain transfer agents on the Au surface where DNA hybridization occurred. A linear polymer growth was observed as a function of the reaction time, characteristic of "living" polymer reactions. Significant improvement in assay sensitivity was realized in comparison to the previously reported polymerization-based sensing method by enhancing polymer growth rate and reducing background noises caused by nonspecific adsorption. Direct visualization of fewer than 2,000 copies of a short oligonucleotide sequence was demonstrated in a detector-free fashion.}, number={10}, journal={ANALYTICAL CHEMISTRY}, author={He, Peng and Zheng, Weiming and Tucker, Eric Z. and Gorman, Christopher B. and He, Lin}, year={2008}, month={May}, pages={3633–3639} }
 @article{lou_he_2008, title={Surface passivation using oligo(ethylene glycol) in ATRP-assisted DNA detection}, volume={129}, ISSN={["0925-4005"]}, DOI={10.1016/j.snb.2007.07.130}, abstractNote={We recently reported a DNA sensing method using polymerization to amplify signal outputs [X. Lou, M.S. Lewis, C.B. Gorman, L. He, Anal. Chem. 77 (2005) 4698–4705]. In the current report an optimization of sensor surface chemistry is conducted in which (S–CH2CH2–OEG6–OMe)2 is used as the preferred surface passivation agent to reduce nonspecific adsorption experienced during ATRP-assisted DNA detection. The presence of oligo(ethylene glycol) (OEG) moieties on the sensor surface significantly reduces background adsorption of proteins, polymers, and reaction monomers used during DNA detection. The level of reduction in background nonspecific adsorption closely depends on the incubation solvent and the incubation time used, as evidenced by the ellipsometric and surface plasmon resonance (SPR) results. Reflectance FTIR results suggest that the surfaces with moderately ordered SAMs exhibit better protein resistance, consistent to the previous observations. Subsequent DNA binding experiments show no apparent decrease in DNA hybridization and ligation efficiencies when OEGylated self-assembled monolayers are used as the passivation layer. Improved DNA detection sensitivity is achieved from reduced background noises.}, number={1}, journal={SENSORS AND ACTUATORS B-CHEMICAL}, author={Lou, Xinhui and He, Lin}, year={2008}, month={Jan}, pages={225–230} }
 @article{guo_he_2007, title={A binary matrix for background suppression in MALDI-MS of small molecules}, volume={387}, ISSN={["1618-2642"]}, DOI={10.1007/s00216-006-1100-3}, abstractNote={Application of matrix-assisted laser-desorption ionization mass spectrometry (MALDI-MS) to small-molecule detection is often limited, because of high matrix background signals in the low-mass region. We report here an approach in which a mixture of two conventional MALDI matrices with different proton affinity was used to suppress the formation of matrix clusters and fragments. Specifically, when acidic alpha-cyano-4-hydroxycinnamic acid (CHCA) and basic 9-aminoacridine (9-AA) were used as the binary matrix, fewer background matrix peaks were observed in both positive and negative-mode detection of small molecules. In addition, the presence of CHCA substantially reduced the laser fluence needed for analyte desorption and ionization; thus better signal-to-background ratios were observed for negatively charged inositol phosphates in complex plant extracts.}, number={5}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Guo, Zhong and He, Lin}, year={2007}, month={Mar}, pages={1939–1944} }
 @article{lou_wang_he_2007, title={Core-shell Au nanoparticle formation with DNA-polymer hybrid coatings using aqueous ATRP}, volume={8}, ISSN={["1525-7797"]}, DOI={10.1021/bm061217+}, abstractNote={We report here a direct surface-grafting approach to forming DNA-containing polymer shells outside of Au nanoparticles using aqueous atom transfer radical polymerization (ATRP). In this approach, DNA molecules were immobilized on Au particles to introduce ATRP initiators on the surface. The same DNA molecules also acted as particle stabilizers through electrostatic repulsion and allowed particles to stay suspended in water. The immobilized ATRP initiators prompted polymer chain growth under certain conditions to form thick polymer shells outside of the particles. The formation of DNA-polymer hybrids outside of Au nanoparticles was characterized using absorption spectroscopy, dynamic light scattering (DLS), transmission electron microscopy (TEM), and gel electrophoresis. The presence of thick polymer shells improved particle stability in high ionic strength media, whereas particles with the DNA coating only aggregated. A visible color difference between these two particle solutions was clearly observed, providing the basis for DNA sensing in homogeneous solutions.}, number={5}, journal={BIOMACROMOLECULES}, author={Lou, Xinhui and Wang, Cuiying and He, Lin}, year={2007}, month={May}, pages={1385–1390} }
 @article{okelo_he_2007, title={Cu(0) as the reaction additive in purge-free ATRP-assisted DNA detection}, volume={23}, DOI={10.1016/j.bios.2007.06.01}, number={4}, journal={Biosensors & Bioelectronics}, author={Okelo, G. O. and He, L.}, year={2007}, pages={588–592} }
 @article{liu_guo_he_2007, title={Mass spectrometry imaging of small molecules using desorption/ionization on silicon}, volume={79}, ISSN={["1520-6882"]}, DOI={10.1021/ac0611465}, abstractNote={Development of novel tools to image spatial distribution of small molecules in biological samples is essential in disease diagnosis and biomarker discovery. To simplify sample preparation and reduce background noise in the low-mass region, we describe here the use of a matrix-free mass spectrometric imaging method, i.e., desorption/ionization on silicon (DIOS), for biological surface analysis. The imaging parameters, such as the laser beam diameter and the translation stage movement, were studied and optimized to improve imaging performance. The use of DIOS imaging to map small molecules on mouse liver tissues was demonstrated. In addition, phosphatidylcholine (PC) and propidium iodide (PI) were used as the cell membrane and nucleus markers, respectively, to "visualize" the presence of HEK 293 cells. The reconstructed ion maps of PC and PI were compared with the optical images collected from the same sample using bright-field and fluorescence microscopy. A good correlation of the spatial distribution of cells confirmed the validity of this DIOS imaging approach.}, number={10}, journal={ANALYTICAL CHEMISTRY}, author={Liu, Qiang and Guo, Zhong and He, Lin}, year={2007}, month={May}, pages={3535–3541} }
 @article{liu_wang_du_sun_he_2007, title={Recognition of glycoprotein peroxidase via con A-carrying self-assembly layer on gold}, volume={8}, ISSN={["1526-4602"]}, DOI={10.1021/bm070232r}, abstractNote={We have successfully fabricated a self-assembled layer of concanavalin A (Con A) on a gold surface for recognition of glycoproteins. The type IV Con A is covalently bound to 11-mercaptoundecanoic acid (MUA) on gold with a 2-(5-norbornene-2,3-dicarboximido)-1,1,3,3-tetramethyluronium tetrafluoroborate (TNTU) linkage. The binding interaction between glycoproteins and self-assembled Con A is studied using horseradish peroxidase (HRP) as a model glycoprotein. Voltammetric, electrochemical impedance studies, and photometric activity measurements show the presence of both specific and nonspecific bindings of HRP to the Con A interface. The specific binding is attributed to the Con A-sugar interaction where Con A selectively recognizes the glycosylation sites of HRP. The catalytic current of the HRP-loaded electrode, because of catalytic oxidation of thionine in the presence of hydrogen peroxide (H2O2), is found to be proportional to the HRP concentrations in the incubation solution. A linear correlation coefficient of 0.993 was obtained over a wide HRP concentration range of 12.5 microg/mL to 1 mg/mL. The approach described in this study provides a simple yet selective means to immobilize glycoproteins on a solid support. The specific binding achieved is desirable in biosensor fabrication, glycoprotein separation, recognition, and purification as well as in drug-releasing systems.}, number={7}, journal={BIOMACROMOLECULES}, author={Liu, Songqin and Wang, Kewei and Du, Dan and Sun, Yueming and He, Lin}, year={2007}, month={Jul}, pages={2142–2148} }
 @article{lou_he_2006, title={DNA-accelerated atom transfer radical polymerization on a gold surface}, volume={22}, ISSN={["0743-7463"]}, DOI={10.1021/la052654x}, abstractNote={A significantly increased polymer growth rate was observed during a surface-initiated ATRP reaction in the presence of DNA molecules. To investigate this phenomenon, thiolated single-stranded DNA molecules (ssDNAs) with ATRP initiators coupled at the distal point were used as the model molecule in the study. In comparison, a small molecule, HS-(CH(2))(11)NHCOC(CH(3))(2)Br, was used to provide a less-polar surface coating for polymer grafting. 2-Hydroxyethyl methacrylate (HEMA) and monomethoxy-capped oligo(ethylene glycol) methacrylate (OEGMA) were used as the ATRP monomers. The polymer growth rates were monitored by measuring the thickness of the polymer films formed at different times. Our results show that the presence of DNA molecules, although at a less-than-1% surface coverage, significantly accelerated the growth rates of both poly(2-hydroxyethyl methacrylate) (PHEMA) and poly(oligoethylene glycol methacrylate) (POEGMA) at the beginning of the ATRP reactions. This accelerating effect was suspected to be a combined result of the highly charged sugar-phosphate backbones of DNA molecules and the formation of Cu complexes with DNA bases. After the initial polymer growth, a smaller yet constant polymer growth rate was observed, suggesting the reduced influence of DNA molecules as the ATRP reaction centers moved farther away from the surface. Similar to conventional ATRP reactions, the polymer growth from surface-anchored DNA molecules was found to be strongly dependent on the composition and the concentration of the catalysts used. Specifically, a catalyst mixture of CuCl/30% CuBr(2)/bpy with 23 mM CuCl was found to provide the optimal reaction condition to yield the fastest polymer film growth among the conditions tested.}, number={6}, journal={LANGMUIR}, author={Lou, XH and He, L}, year={2006}, month={Mar}, pages={2640–2646} }
 @misc{guo_ganawi_liu_he_2006, title={Nanomaterials in mass spectrometry ionization and prospects for biological application}, volume={384}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-005-0125-3}, abstractNote={The rapid development of nanotechnology has revolutionized scientific developments in recent decades. Mass spectrometry (MS) measurements are no exception and have benefited greatly from integration of nanomaterials in every step of analysis. This brief review summarizes recent developments in the field with the focus on the use of nanomaterials as alternative media to facilitate analyte ionization in laser-desorption ionization-mass spectrometry (LDI-MS) and secondary ion mass spectrometry (SIMS). The biological applications of both techniques are also detailed. The use of nanomaterials in other aspects of MS analysis, for example in sample clean-up and indirect analyte quantification, is briefly discussed.}, number={3}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Guo, Z and Ganawi, AAA and Liu, Q and He, L}, year={2006}, month={Feb}, pages={584–592} }
 @misc{lou_he_okelo_he_2006, title={Radical polymerization in biosensing}, volume={386}, ISSN={["1618-2642"]}, DOI={10.1007/s00216-006-0576-1}, abstractNote={This review briefly summarizes recently published work on radical polymerization in biosensor-related applications. Advancements in surface modification aimed at improving sensor biocompatibility and reducing nonspecific background noises are discussed. Direct applications of polymers as one of the key sensing elements in which they are used either as detection probes for the biomolecular binding events or as signal transducers to amplify sensing signals are detailed. Initial applications of radical polymerization reactions in biosensing are evident and appear promising.}, number={3}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Lou, Xinhui and He, Peng and Okelo, Geoffrey O. and He, Lin}, year={2006}, month={Oct}, pages={525–531} }
 @article{lou_lewis_gorman_he_2005, title={Detection of DNA point mutation by atom transfer radical polymerization}, volume={77}, ISSN={["1520-6882"]}, DOI={10.1021/ac050706h}, abstractNote={We report here a new DNA detection method in which polymer growth in atom transfer radical polymerization (ATRP) is used as a means to amplify detection signals. In this method, DNA hybridization and ligation reactions led to the attachment of ATRP initiators on a solid surface where specific DNA sequences were located. These initiators subsequently triggered the growth of poly(hydroxyethyl methacrylate) (PHEMA) at the end of immobilized DNA molecules and formed polymer brushes. The formation of PHEMA altered substrate opacity, rendering the corresponding spots readily distinguishable to the naked eye. A second ATRP reaction to form branched polymers on the surface drastically improved the visibility of DNA hybridization and significantly shortened the detection time. The resulting polymer film was characterized using infrared spectroscopy, ellipsometry, contact angle measurements, and atomic force microscopy. Direct visualization of 1 fmol of target DNA molecules of interest was demonstrated. A proof-of-principle experiment to detect DNA point mutation was conducted. The perfectly matched DNA targets were distinctively differentiated from those with mutations. The demonstrated capability to detect DNA mutation with direct visualization laid the groundwork for the future development of detector-free testing kits in single-nucleotide polymorphism screenings.}, number={15}, journal={ANALYTICAL CHEMISTRY}, author={Lou, XH and Lewis, MS and Gorman, CB and He, L}, year={2005}, month={Aug}, pages={4698–4705} }
 @article{finkel_prevo_velev_he_2005, title={Ordered silicon nanocavity arrays in surface-assisted desorption/ionization mass spectrometry}, volume={77}, ISSN={["1520-6882"]}, url={http://www.scopus.com/inward/record.url?eid=2-s2.0-13844320727&partnerID=MN8TOARS}, DOI={10.1021/ac048645v}, abstractNote={We report here a simple method to generate ordered nanocavity arrays on a Si wafer and use it in surface-assisted laser desorption/ionization mass spectrometry (SALDI-MS). A close-packed SiO2 nanosphere array was first deposited on a low-resistivity Si wafer using a convective self-assembly method. The nanoparticle array was then used as a mask in a reactive ion etching (RIE) process to selectively remove portions of the Si surface. Subsequent sonication removed those physically adsorbed SiO2 nanoparticles and exposed an ordered nanocavity array underneath. The importance of this approach is its capability of systematically varying surface geometries to achieve desired features, which makes detailed studies of the impacts of surface features on the desorption/ionization mechanism feasible. We demonstrated that the in-plane width and out-of-plane depth of the cavities were adjustable by varying etching times, and the intercavity spacing was controllable by varying the number of particle layers deposited. MS detection of small peptides on these substrates showed comparable sensitivity to conventional porous Si substrates (DIOS, desorption/ ionization on porous silicon). The desorption and ionization efficiency of these roughened surfaces exhibited a nonmonotonic relationship to the increased total surface area. Several possible factors contributing to the observed phenomenon are speculated upon. The application of this arrayed surface in metabolite detection of Arabidopsis thaliana root extracts is also demonstrated.}, number={4}, journal={ANALYTICAL CHEMISTRY}, author={Finkel, NH and Prevo, BG and Velev, OD and He, L}, year={2005}, month={Feb}, pages={1088–1095} }
 @article{finkel_lou_wang_he_2004, title={Barcoding the microworld}, volume={76}, number={19}, journal={Analytical Chemistry}, author={Finkel, N. H. and Lou, X. H. and Wang, C. Y. and He, L.}, year={2004}, pages={353A–359} }
 @article{he_smith_natan_keating_2004, title={The distance-dependence of colloidal Au-amplified surface plasmon resonance}, volume={108}, ISSN={["1520-5207"]}, DOI={10.1021/jp048536k}, abstractNote={Au nanoparticle-amplified surface plasmon resonance (PA-SPR), like traditional SPR, is typically used to detect binding events at a thin noble metal film. Here we describe the use of SiO2-overcoated Au films as a substrate for PA-SPR. Changes in SPR angle shift upon Au nanosphere binding were investigated as a function of the SiO2 thickness. In these experiments, a submonolayer of Au nanoparticles was immobilized atop a thin Au film separated by an intervening SiO2 layer. Although SPR is an evanescent wave technique, the observed SPR angle shift does not decrease monotonically with increasing Au nanoparticle−Au surface separation, but rather increases to a maximum at ∼32 nm separation before decreasing. In contrast to the previously proposed electromagnetic coupling between the metal particles and the surface as the main cause for the observed distance-dependent SPR response, we propose and have demonstrated qualitatively that the energy modulating capability of the SiO2 spacing layer is the main contribu...}, number={30}, journal={JOURNAL OF PHYSICAL CHEMISTRY B}, author={He, L and Smith, EA and Natan, MJ and Keating, CD}, year={2004}, month={Jul}, pages={10973–10980} }
 @misc{penn_he_natan_2003, title={Nanoparticles for bioanalysis}, volume={7}, number={5}, journal={Current Opinion in Chemical Biology}, author={Penn, S. G. and He, L. and Natan, M. J.}, year={2003}, pages={609–615} }