@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{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{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{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} }