@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} }
 @misc{giri_pandey_shrestha_pokharel_ligler_neupane_2021, title={Review of analytical performance of COVID-19 detection methods}, volume={413}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-020-02889-x}, abstractNote={In the recent SARS-CoV-2 pandemic, public health experts have emphasized testing, tracking infected people, and tracing their contacts as an effective strategy to reduce the spread of the virus. Several diagnostic methods are reported for detecting the coronavirus in clinical, research, and public health laboratories. Some tests detect the infection directly by detecting the viral RNA and other tests detect the infection indirectly by detecting the host antibodies. A diagnostic test during the pandemic should help make an appropriate clinical decision in a short period of time. Recently reported diagnostic methods for SARS-CoV-2 have varying throughput, batching capacity, requirement of infrastructure setting, analytical performance, and turnaround times ranging from a few minutes to several hours. These factors should be considered while selecting a reliable and rapid diagnostic method to help make an appropriate decision and prompt public health interventions. This paper reviews recent SARS-CoV-2 diagnostic methods published in journals and reports released by regulatory agencies. We compared the analytical efficiency including limit of detection, sensitivity, specificity, and throughput. In addition, we also looked into ease of use, affordability, and availability of accessories. Finally, we discuss the limitations of the methods and provide our perspectives on priorities for future test development.}, number={1}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Giri, Basant and Pandey, Shishir and Shrestha, Retina and Pokharel, Krisha and Ligler, Frances S. and Neupane, Bhanu B.}, year={2021}, month={Jan}, pages={35–48} }
 @article{neupane_zhong_wang_2020, title={Study on self-assembly of colloidal particles at high ionic strength with stimulated emission depletion microscopy}, volume={2}, ISSN={["2577-8196"]}, DOI={10.1002/eng2.12233}, abstractNote={Understanding the spatial organization of nano‐ and micro‐sized particle is very important in the fabrication of complex structures having unprecedented properties. Study on self‐assembly of submicroscopic colloidal particles at high ionic strength solution at single particle resolution can provide new insight into the nanoscale interactions. In this study, we studied the self assembly behavior of negatively charged 0.2 and 1 μm colloidal particles at high ionic strength on glass‐solution interface that is, in situ environment. The self‐assembled 0.2 μm particles could not be resolved with conventional confocal and epi‐fluorescent microscopy, so a home‐built continuous wave stimulated emission depletion (STED) microscope was used for the study. We found that particles self‐assemble into ordered and disordered structures at higher and lower ionic strength solution, respectively. The optical imaging methods allowed us to measure inter‐particle gap at second energy minimum directly. Interestingly, we found that the inter‐particle gap in the wet self‐assembly higher than the classical Derjaguin, Landau, Verwey, and Overbeek (DLVO) theory predicted. The in situ investigation of particle self‐assembly at high ionic strength will provide more insight for the understanding nanoscale interactions.}, number={9}, journal={ENGINEERING REPORTS}, author={Neupane, Bhanu B. and Zhong, Yaning and Wang, Gufeng}, year={2020}, month={Sep} }
 @article{chen_neupane_li_su_wang_2016, title={Investigating axial diffusion in cylindrical pores using confocal single-particle fluorescence correlation spectroscopy}, volume={37}, ISSN={["1522-2683"]}, DOI={10.1002/elps.201600158}, abstractNote={We explored the feasibility of using confocal fluorescence correlation spectroscopy to study small nanoparticle diffusion in hundred‐nanometer‐sized cylindrical pores. By modeling single particle diffusion in tube‐like confined three‐dimensional space aligned parallel to the confocal optical axis, we showed that two diffusion dynamics can be observed in both original intensity traces and the autocorrelation functions (ACFs): the confined two‐dimensional lateral diffusion and the unconfined one‐dimensional (1D) axial diffusion. The separation of the axial and confined lateral diffusion dynamics provides an opportunity to study diffusions in different dimensions separately. We further experimentally studied 45 nm carboxylated polystyrene particles diffusing in 300 nm alumina pores. The experimental data showed consistency with the simulation. To extract the accurate axial diffusion coefficient, we found that a 1D diffusion model with a Lorentzian axial collection profile needs to be used to analyze the experimental ACFs. The diffusion of the 45 nm nanoparticles in polyethyleneglycol‐passivated 300 nm pores slowed down by a factor of ∼2, which can be satisfactorily explained by hydrodynamic frictions.}, number={15-16}, journal={ELECTROPHORESIS}, author={Chen, Fang and Neupane, Bhanu and Li, Peiyuan and Su, Wei and Wang, Gufeng}, year={2016}, month={Aug}, pages={2129–2138} }
 @article{chen_garcia-lopez_jin_neupane_chu_tour_wang_2016, title={Moving Kinetics of Nanocars with Hydrophobic Wheels on Solid Surfaces at Ambient Conditions}, volume={120}, ISSN={["1932-7447"]}, DOI={10.1021/acs.jpcc.6b01249}, abstractNote={Motivated by “driving” nanoscopic nanocars on solid substrate surfaces at ambient conditions, we studied the moving kinetics of nanocars on differently modified surfaces. Single molecule fluorescence imaging was used to track the nanocar movement so that the molecules were minimally perturbed. On freshly cleaned, hydroxylated glass surfaces, nanocars with hydrophobic adamantane wheels can diffuse with a relatively large diffusion coefficient of 7.6 × 10–16 m2/s. Both the number of moving molecules and the mobility of the moving molecules decreased over time when the sample was exposed in the air. Similar declinations in movement were observed on a poly(ethylene glycol) (PEG)-modified glass surface, but the declination rate was lowered. The slowing of molecular surface diffusion is correlated to the hydrophobicity of the surface and is likely caused by the adsorption of hydrophobic molecules from the air. A proposed sticky-spots model explains the decreasing apparent diffusion coefficient of the hydrophobi...}, number={20}, journal={JOURNAL OF PHYSICAL CHEMISTRY C}, author={Chen, Fang and Garcia-Lopez, Victor and Jin, Tao and Neupane, Bhanu and Chu, Pin-Lei E. and Tour, James and Wang, Gufeng}, year={2016}, month={May}, pages={10887–10894} }
 @article{neupane_chen_wei_fang_ligler_wang_2016, title={Nanosecond Time-Resolution Study of Gold Nanorod Rotation at the Liquid-Solid Interface}, volume={17}, ISSN={["1439-7641"]}, DOI={10.1002/cphc.201600174}, abstractNote={Early studies showed that the adsorption of nanorods may start from a special "anchored" state, in which the nanorods lose translational motion but retain rotational freedom. Insight into how the anchored nanorods rotate should provide additional dimensions for understanding particle-surface interactions. Based on conventional time-resolution studies, gold nanorods are thought to continuously rotate following initial interactions with negatively charged glass surfaces. However, this nanosecond time-resolution study reveals that the apparent continuous rotation actually consists of numerous fast, intermittent rotations or transitions between a small number of weakly immobilized states, with the particle resting in the immobilized states most of the time. The actual rotation from one immobilized state to the other happens on a 1 ms timescale, that is, approximately 50 times slower than in the bulk solution.}, number={14}, journal={CHEMPHYSCHEM}, author={Neupane, Bhanu and Chen, Fang and Wei, Yanli and Fang, Ning and Ligler, Frances S. and Wang, Gufeng}, year={2016}, month={Jul}, pages={2218–2224} }
 @article{pacardo_neupane_rikard_lu_mo_mishra_tracy_wang_ligler_gu_2015, title={A dual wavelength-activatable gold nanorod complex for synergistic cancer treatment}, volume={7}, ISSN={["2040-3372"]}, url={http://gateway.webofknowledge.com/gateway/Gateway.cgi?GWVersion=2&SrcAuth=ORCID&SrcApp=OrcidOrg&DestLinkType=FullRecord&DestApp=WOS_CPL&KeyUT=WOS:000357805700034&KeyUID=WOS:000357805700034}, DOI={10.1039/c5nr01568e}, abstractNote={A multifunctional gold nanorod (AuNR) complex is described with potential utility for theranostic anticancer treatment. The AuNR was functionalized with cyclodextrin for encapsulation of doxorubicin, with folic acid for targeting, and with a photo-responsive dextran-azo compound for intracellular controlled drug release. The interaction of a AuNR complex with HeLa cells was facilitated via a folic acid targeting ligand as displayed in the dark-field images of cells. Enhanced anticancer efficacy was demonstrated through the synergistic combination of promoted drug release upon ultraviolet (UV) light irradiation and photothermal therapy upon infrared (IR) irradiation. This multifunctional AuNR-based system represents a novel theranostic strategy for spatiotemporal delivery of anticancer therapeutics.}, number={28}, journal={NANOSCALE}, author={Pacardo, Dennis B. and Neupane, Bhanu and Rikard, S. Michaela and Lu, Yue and Mo, Ran and Mishra, Sumeet R. and Tracy, Joseph B. and Wang, Gufeng and Ligler, Frances S. and Gu, Zhen}, year={2015}, pages={12096–12103} }
 @article{pacardo_neupane_wang_gu_walker_ligler_2015, title={A temperature microsensor for measuring laser-induced heating in gold nanorods}, volume={407}, ISSN={["1618-2650"]}, DOI={10.1007/s00216-014-8222-9}, number={3}, journal={ANALYTICAL AND BIOANALYTICAL CHEMISTRY}, author={Pacardo, Dennis B. and Neupane, Bhanu and Wang, Gufeng and Gu, Zhen and Walker, Glenn M. and Ligler, Frances S.}, year={2015}, month={Jan}, pages={719–725} }
 @article{neupane_jin_mellor_loboa_ligler_wang_2015, title={Continuous-wave stimulated emission depletion microscope for imaging actin cytoskeleton in fixed and live cells}, volume={15}, number={9}, journal={Sensors (Basel, Switzerland)}, author={Neupane, B. and Jin, T. and Mellor, L. F. and Loboa, E. G. and Ligler, F. S. and Wang, G. F.}, year={2015}, pages={24178–24190} }
 @misc{neupane_ligler_wang_2014, title={Review of recent developments in stimulated emission depletion microscopy: Applications on cell imaging}, volume={19}, number={8}, journal={Journal of Biomedical Optics}, author={Neupane, B. and Ligler, F. S. and Wang, G. F.}, year={2014} }
 @misc{stender_marchuk_liu_sander_meyer_smith_neupane_wang_li_cheng_et al._2013, title={Single Cell Optical Imaging and Spectroscopy}, volume={113}, ISSN={["1520-6890"]}, DOI={10.1021/cr300336e}, abstractNote={In his 1665 treatise, Micrographia, Robert Hooke described the many observations he had made using a microscope, including compartment-like structures in cork samples that he termed ‘cells’.1 In the three and a half centuries since Hooke’s day, both the microscope and our understanding of the cell have been vastly improved upon, and the current outlook suggests that the symbiotic relationship between the microscope and the cell will continue to flourish into the foreseeable future. The cell is a basic yet complicated ‘unit’ of interest to biology, just as the atom is to chemists. Ultimately, scientists want to ‘see to believe’ when it comes to an explanation of the complex inner workings of cells, but therein lies a complication. Seeing is not always a possibility in biological systems. Size, speed, sensitivity, and additional concerns plague the microscopist who wants to peek inside of a cell. Enter a variety of molecular and nanoparticle probes that are capable of tagging and pinpointing the location of biological components that would otherwise be invisible under the microscope. Advances in laser, camera, and imaging processing technologies have also played a crucial role in the burgeoning field of single cell imaging, because they have brought into view the fast processes that would normally escape the human eye. 
 
The purpose of this review is to highlight the key advances that have occurred in the past several years in the field of single cell optical imaging. It is not our intent to provide a comprehensive review of the types of experiments or the areas of cell research that are ongoing. Reviews with a distinctly biological flavor have been published recently, and these alternative reviews focus on specific details of the cell and the processes that occur within.2-7 Likewise, exceptional review papers that have discussed the full spectrum of nanoparticle probes and their properties have appeared recently.6-12 This review is designed to give an overview of the tools that are being specifically used to accomplish single cell imaging. As such, much of our emphasis in the first several sections of this paper is on imaging platforms, with a focus on design details that are important to single cell imaging experiments. Next we emphasize specific imaging experiments that highlight the types of findings that are possible at the nexus of microscopy, nanoprobes, and live cells. Particular attention is paid to the emerging orientation and rotational tracking of single probes linked to mechanistic functions and differentiated structures of biological interest. Finally, we provide a brief, yet rather complete, summary of single cell manipulation techniques.}, number={4}, journal={CHEMICAL REVIEWS}, author={Stender, Anthony S. and Marchuk, Kyle and Liu, Chang and Sander, Suzanne and Meyer, Matthew W. and Smith, Emily A. and Neupane, Bhanu and Wang, Gufeng and Li, Junjie and Cheng, Ji-Xin and et al.}, year={2013}, month={Apr}, pages={2469–2527} }
 @article{neupane_chen_sun_chiu_wang_2013, title={Tuning donut profile for spatial resolution in stimulated emission depletion microscopy}, volume={84}, number={4}, journal={Review of Scientific Instruments}, author={Neupane, B. and Chen, F. and Sun, W. and Chiu, D. T. and Wang, G. F.}, year={2013} }
 @article{neupane_zhao_wang_2013, title={Up-Conversion Luminescence of Gold Nanospheres When Excited at Nonsurface Plasmon Resonance Wavelength by a Continuous Wave Laser}, volume={13}, ISSN={["1530-6992"]}, DOI={10.1021/nl401505p}, abstractNote={We show that, when gold nanospheres are excited at the red side of the surface plasmon resonance (SPR) wavelength at 592 nm by a continuous wave (CW) laser, they give substantial up-converted luminescence in the SPR wavelength range. The luminescence intensity scales as a second-order function of the excitation power, with a quantum yield ~1/50 of down-conversion luminescence when illuminated at a power of 30 MW/cm(2). The luminescence spectrum is completely different than the SPR profile, indicating a new emission mechanism possibly involving interband transitions coupled with phonons or localized vibration of neighboring gold atoms. Such luminescence is also observed to be substantial for short gold nanorods with an aspect ratio of ~2 but weak for bulk gold. This study provides new insight to the understanding of gold nanoparticle luminescence and opens a new detection scheme for gold nanoparticle-based biological imaging.}, number={9}, journal={NANO LETTERS}, author={Neupane, Bhanu and Zhao, Luyang and Wang, Gufeng}, year={2013}, month={Sep}, pages={4087–4092} }