Skip to main content

Kevin D. Welsher

Robert R. & Katherine B. Penn Associate Professor
Chemistry
Box 90348, Durham, NC 27708
2213 French Science Center, Durham, NC 27705

Selected Publications


Active-Feedback 3D Single-Molecule Tracking Using a Fast-Responding Galvo Scanning Mirror.

Journal Article The journal of physical chemistry. A · August 2023 Real-time three-dimensional single-particle tracking (RT-3D-SPT) allows continuous detection of individual freely diffusing objects with high spatiotemporal precision by applying closed-loop active feedback in an optical microscope. However, the current tr ... Full text Cite

The trajectory patterns of single HIV-1 virus-like particle in live CD4 cells: A real time three-dimensional multi-resolution microscopy study using encapsulated nonblinking giant quantum dot.

Journal Article Journal of microbiology, immunology, and infection = Wei mian yu gan ran za zhi · April 2023 BackgroundThe exploration of virology knowledge was limited by the optical technology for the observation of virus. Previously, a three-dimensional multi-resolution real-time microscope system (3D-MRM) was developed to observe the uptake of HIV-1- ... Full text Cite

Using COBWEBS for 3D active-feedback tracking of freely diffusing particles in tricky environments

Conference Progress in Biomedical Optics and Imaging - Proceedings of SPIE · January 1, 2023 Active-feedback 3D single-particle tracking in complex environments is limited to bright slow-moving subjects. Extending this technique to include complex background environments requires the development of particle localization strategies that can account ... Full text Cite

Data from: Mapping nanoscale forces and potentials in live cells with microsecond 3D single-particle tracking

Dataset · December 9, 2022 3D single-particle tracking has the potential to resolve the molecular-level forces that dictate particle motion in biological systems. However, the information gleaned from 3D single-particle tracking often cannot resolve underlying nanoscale potentials d ... Full text Cite

Capturing the start point of the virus-cell interaction with high-speed 3D single-virus tracking.

Journal Article Nature methods · December 2022 The early stages of the virus-cell interaction have long evaded observation by existing microscopy methods due to the rapid diffusion of virions in the extracellular space and the large three-dimensional cellular structures involved. Here we present an act ... Full text Cite

Combined online Bayesian and windowed estimation of background and signal localization facilitates active-feedback particle tracking in complex environments.

Journal Article The Journal of chemical physics · November 2022 Despite successes in tracking single molecules in vitro, the extension of active-feedback single-particle methods to tracking rapidly diffusing and unconfined proteins in live cells has not been realized. Since the existing active-feedback localization met ... Full text Cite

Engineering Lipid Nanoparticles for Enhanced Intracellular Delivery of mRNA through Inhalation.

Journal Article ACS nano · September 2022 Despite lipid nanoparticles' (LNPs) success in the effective and safe delivery of mRNA vaccines, an inhalation-based mRNA therapy for lung diseases remains challenging. LNPs tend to disintegrate due to shear stress during aerosolization, leading to ineffec ... Full text Cite

Growth Kinetics of Single Polymer Particles in Solution via Active-Feedback 3D Tracking.

Journal Article Journal of the American Chemical Society · August 2022 The ability to directly observe chemical reactions at the single-molecule and single-particle level has enabled the discovery of behaviors otherwise obscured by ensemble averaging in bulk measurements. However powerful, a common restriction of these studie ... Full text Cite

Particle-by-Particle In Situ Characterization of the Protein Corona via Real-Time 3D Single-Particle-Tracking Spectroscopy*.

Journal Article Angewandte Chemie (International ed. in English) · October 2021 Nanoparticles (NPs) adsorb proteins when exposed to biological fluids, forming a dynamic protein corona that affects their fate in biological environments. A comprehensive understanding of the protein corona is lacking due to the inability of current techn ... Full text Cite

Information-Efficient, Off-Center Sampling Results in Improved Precision in 3D Single-Particle Tracking Microscopy.

Journal Article Entropy (Basel, Switzerland) · April 2021 In this work, we present a 3D single-particle tracking system that can apply tailored sampling patterns to selectively extract photons that yield the most information for particle localization. We demonstrate that off-center sampling at locations predicted ... Full text Cite

Author Correction: Naturally-occurring cholesterol analogues in lipid nanoparticles induce polymorphic shape and enhance intracellular delivery of mRNA.

Journal Article Nature communications · July 2020 Featured Publication An amendment to this paper has been published and can be accessed via a link at the top of the paper. ... Full text Cite

Real-time 3D single molecule tracking.

Journal Article Nature communications · July 2020 Featured Publication To date, single molecule studies have been reliant on tethering or confinement to achieve long duration and high temporal resolution measurements. Here, we present a 3D single-molecule active real-time tracking method (3D-SMART) which is capable of locking ... Full text Cite

Mapping solvation heterogeneity in live cells by hyperspectral stimulated Raman scattering microscopy.

Journal Article The Journal of chemical physics · May 2020 Water provides a dynamic matrix in which all biochemical processes occur in living organisms. The structure and dynamics of intracellular water constitute the cornerstone for understanding all aspects of cellular function. Fundamentally, direct visualizati ... Full text Cite

Naturally-occurring cholesterol analogues in lipid nanoparticles induce polymorphic shape and enhance intracellular delivery of mRNA.

Journal Article Nature communications · February 2020 Featured Publication Endosomal sequestration of lipid-based nanoparticles (LNPs) remains a formidable barrier to delivery. Herein, structure-activity analysis of cholesterol analogues reveals that incorporation of C-24 alkyl phytosterols into LNPs (eLNPs) enhances gene transfe ... Full text Cite

Continuous focal translation enhances rate of point-scan volumetric microscopy.

Journal Article Optics express · December 2019 Two-Photon Laser-Scanning Microscopy is a powerful tool for exploring biological structure and function due to its ability to optically section through a sample with a tight focus. While it is possible to obtain 3D image stacks by moving a stage, this per- ... Full text Cite

An Adaptive Real-Time 3D Single Particle Tracking Method for Monitoring Viral First Contacts.

Journal Article Small (Weinheim an der Bergstrasse, Germany) · October 2019 Here, an adaptive real-time 3D single particle tracking method is proposed, which is capable of capturing heterogeneous dynamics. Using a real-time measurement of a rapidly diffusing particle's positional variance, the 3D precision adaptive real-time track ... Full text Cite

Point-scan volumetric imaging rate increased by an optimized linear sparse sampling pattern

Conference Frontiers in Optics - Proceedings Frontiers in Optics + Laser Science APS/DLS · September 8, 2019 Conventional point-scan volumetric imaging requires long acquisition times. Constant focal scanning during a 2D frame scan creates sparse 3D patterns enabling up to 4x speed increase through interpolation as implemented in a two-photon microscope. ... Full text Cite

Real-Time 3D Single Particle Tracking: Towards Active Feedback Single Molecule Spectroscopy in Live Cells.

Journal Article Molecules (Basel, Switzerland) · August 2019 Single molecule fluorescence spectroscopy has been largely implemented using methods which require tethering of molecules to a substrate in order to make high temporal resolution measurements. However, the act of tethering a molecule requires that the mole ... Full text Cite

A Protocol for Real-time 3D Single Particle Tracking.

Journal Article Journal of visualized experiments : JoVE · January 2018 Real-time three-dimensional single particle tracking (RT-3D-SPT) has the potential to shed light on fast, 3D processes in cellular systems. Although various RT-3D-SPT methods have been put forward in recent years, tracking high speed 3D diffusing particles ... Full text Cite

Active-Feedback 3D Single-Molecule Tracking Using a Fast-Responding Galvo Scanning Mirror.

Journal Article The journal of physical chemistry. A · August 2023 Real-time three-dimensional single-particle tracking (RT-3D-SPT) allows continuous detection of individual freely diffusing objects with high spatiotemporal precision by applying closed-loop active feedback in an optical microscope. However, the current tr ... Full text Cite

The trajectory patterns of single HIV-1 virus-like particle in live CD4 cells: A real time three-dimensional multi-resolution microscopy study using encapsulated nonblinking giant quantum dot.

Journal Article Journal of microbiology, immunology, and infection = Wei mian yu gan ran za zhi · April 2023 BackgroundThe exploration of virology knowledge was limited by the optical technology for the observation of virus. Previously, a three-dimensional multi-resolution real-time microscope system (3D-MRM) was developed to observe the uptake of HIV-1- ... Full text Cite

Using COBWEBS for 3D active-feedback tracking of freely diffusing particles in tricky environments

Conference Progress in Biomedical Optics and Imaging - Proceedings of SPIE · January 1, 2023 Active-feedback 3D single-particle tracking in complex environments is limited to bright slow-moving subjects. Extending this technique to include complex background environments requires the development of particle localization strategies that can account ... Full text Cite

Data from: Mapping nanoscale forces and potentials in live cells with microsecond 3D single-particle tracking

Dataset · December 9, 2022 3D single-particle tracking has the potential to resolve the molecular-level forces that dictate particle motion in biological systems. However, the information gleaned from 3D single-particle tracking often cannot resolve underlying nanoscale potentials d ... Full text Cite

Capturing the start point of the virus-cell interaction with high-speed 3D single-virus tracking.

Journal Article Nature methods · December 2022 The early stages of the virus-cell interaction have long evaded observation by existing microscopy methods due to the rapid diffusion of virions in the extracellular space and the large three-dimensional cellular structures involved. Here we present an act ... Full text Cite

Combined online Bayesian and windowed estimation of background and signal localization facilitates active-feedback particle tracking in complex environments.

Journal Article The Journal of chemical physics · November 2022 Despite successes in tracking single molecules in vitro, the extension of active-feedback single-particle methods to tracking rapidly diffusing and unconfined proteins in live cells has not been realized. Since the existing active-feedback localization met ... Full text Cite

Engineering Lipid Nanoparticles for Enhanced Intracellular Delivery of mRNA through Inhalation.

Journal Article ACS nano · September 2022 Despite lipid nanoparticles' (LNPs) success in the effective and safe delivery of mRNA vaccines, an inhalation-based mRNA therapy for lung diseases remains challenging. LNPs tend to disintegrate due to shear stress during aerosolization, leading to ineffec ... Full text Cite

Growth Kinetics of Single Polymer Particles in Solution via Active-Feedback 3D Tracking.

Journal Article Journal of the American Chemical Society · August 2022 The ability to directly observe chemical reactions at the single-molecule and single-particle level has enabled the discovery of behaviors otherwise obscured by ensemble averaging in bulk measurements. However powerful, a common restriction of these studie ... Full text Cite

Particle-by-Particle In Situ Characterization of the Protein Corona via Real-Time 3D Single-Particle-Tracking Spectroscopy*.

Journal Article Angewandte Chemie (International ed. in English) · October 2021 Nanoparticles (NPs) adsorb proteins when exposed to biological fluids, forming a dynamic protein corona that affects their fate in biological environments. A comprehensive understanding of the protein corona is lacking due to the inability of current techn ... Full text Cite

Information-Efficient, Off-Center Sampling Results in Improved Precision in 3D Single-Particle Tracking Microscopy.

Journal Article Entropy (Basel, Switzerland) · April 2021 In this work, we present a 3D single-particle tracking system that can apply tailored sampling patterns to selectively extract photons that yield the most information for particle localization. We demonstrate that off-center sampling at locations predicted ... Full text Cite

Author Correction: Naturally-occurring cholesterol analogues in lipid nanoparticles induce polymorphic shape and enhance intracellular delivery of mRNA.

Journal Article Nature communications · July 2020 Featured Publication An amendment to this paper has been published and can be accessed via a link at the top of the paper. ... Full text Cite

Real-time 3D single molecule tracking.

Journal Article Nature communications · July 2020 Featured Publication To date, single molecule studies have been reliant on tethering or confinement to achieve long duration and high temporal resolution measurements. Here, we present a 3D single-molecule active real-time tracking method (3D-SMART) which is capable of locking ... Full text Cite

Mapping solvation heterogeneity in live cells by hyperspectral stimulated Raman scattering microscopy.

Journal Article The Journal of chemical physics · May 2020 Water provides a dynamic matrix in which all biochemical processes occur in living organisms. The structure and dynamics of intracellular water constitute the cornerstone for understanding all aspects of cellular function. Fundamentally, direct visualizati ... Full text Cite

Naturally-occurring cholesterol analogues in lipid nanoparticles induce polymorphic shape and enhance intracellular delivery of mRNA.

Journal Article Nature communications · February 2020 Featured Publication Endosomal sequestration of lipid-based nanoparticles (LNPs) remains a formidable barrier to delivery. Herein, structure-activity analysis of cholesterol analogues reveals that incorporation of C-24 alkyl phytosterols into LNPs (eLNPs) enhances gene transfe ... Full text Cite

Continuous focal translation enhances rate of point-scan volumetric microscopy.

Journal Article Optics express · December 2019 Two-Photon Laser-Scanning Microscopy is a powerful tool for exploring biological structure and function due to its ability to optically section through a sample with a tight focus. While it is possible to obtain 3D image stacks by moving a stage, this per- ... Full text Cite

An Adaptive Real-Time 3D Single Particle Tracking Method for Monitoring Viral First Contacts.

Journal Article Small (Weinheim an der Bergstrasse, Germany) · October 2019 Here, an adaptive real-time 3D single particle tracking method is proposed, which is capable of capturing heterogeneous dynamics. Using a real-time measurement of a rapidly diffusing particle's positional variance, the 3D precision adaptive real-time track ... Full text Cite

Point-scan volumetric imaging rate increased by an optimized linear sparse sampling pattern

Conference Frontiers in Optics - Proceedings Frontiers in Optics + Laser Science APS/DLS · September 8, 2019 Conventional point-scan volumetric imaging requires long acquisition times. Constant focal scanning during a 2D frame scan creates sparse 3D patterns enabling up to 4x speed increase through interpolation as implemented in a two-photon microscope. ... Full text Cite

Real-Time 3D Single Particle Tracking: Towards Active Feedback Single Molecule Spectroscopy in Live Cells.

Journal Article Molecules (Basel, Switzerland) · August 2019 Single molecule fluorescence spectroscopy has been largely implemented using methods which require tethering of molecules to a substrate in order to make high temporal resolution measurements. However, the act of tethering a molecule requires that the mole ... Full text Cite

A Protocol for Real-time 3D Single Particle Tracking.

Journal Article Journal of visualized experiments : JoVE · January 2018 Real-time three-dimensional single particle tracking (RT-3D-SPT) has the potential to shed light on fast, 3D processes in cellular systems. Although various RT-3D-SPT methods have been put forward in recent years, tracking high speed 3D diffusing particles ... Full text Cite

Robust real-time 3D single-particle tracking using a dynamically moving laser spot.

Journal Article Optics letters · June 2017 Real-time three-dimensional (3D) single-particle tracking uses optical feedback to lock on to freely diffusing nanoscale fluorescent particles, permitting precise 3D localization and continuous spectroscopic interrogation. Here we describe a new method of ... Full text Cite

Discovery of protein- and DNA-imperceptible nanoparticle hard coating using gel-based reaction tuning.

Journal Article Journal of the American Chemical Society · January 2015 The seemingly inevitable protein corona appears to be an insurmountable obstacle to wider application of functional nanomaterials in biotechnology. The accumulation of serum proteins can block targeting functionalities and alter the in vivo fate of these n ... Full text Cite

Imaging the behavior of molecules in biological systems: breaking the 3D speed barrier with 3D multi-resolution microscopy.

Journal Article Faraday discussions · January 2015 The overwhelming effort in the development of new microscopy methods has been focused on increasing the spatial and temporal resolution in all three dimensions to enable the measurement of the molecular scale phenomena at the heart of biological processes. ... Full text Cite

Multi-resolution 3D visualization of the early stages of cellular uptake of peptide-coated nanoparticles.

Journal Article Nature nanotechnology · March 2014 A detailed understanding of the cellular uptake process is essential to the development of cellular delivery strategies and to the study of viral trafficking. However, visualization of the entire process, encompassing the fast dynamics (local to the freely ... Full text Cite

Three-dimensional target-locking microscopy

Journal Article Optics InfoBase Conference Papers · January 1, 2013 Three-dimensional target-locking microscopy (3D-TLM) is developed to observe the dynamics of fast moving nanoscale particles with high temporal (10 μsec) and spatial (10 nm) definitions while simultaneously imaging the 3D biological environment. © OSA 2013 ... Cite

Three-dimensional target-locking microscopy

Conference Optics InfoBase Conference Papers · January 1, 2013 Three-dimensional target-locking microscopy (3D-TLM) is developed to observe the dynamics of fast moving nanoscale particles with high temporal (10 μsec) and spatial (10 nm) definitions while simultaneously imaging the 3D biological environment. © OSA 2013 ... Full text Cite

Model-free analysis of time-dependent single-molecule spectroscopy: Dynamics of biological macromolecules

Journal Article Proceedings - International Symposium on Biomedical Imaging · August 15, 2012 Rigorous and unbiased statistical analysis of singlemolecule data is now recognized as a crucial component to substantiate any discovery made through such experiments. This presentation summarizes many such tools, and ventures some future directions in the ... Full text Cite

Graphite-coated magnetic nanoparticle microarray for few-cells enrichment and detection.

Journal Article ACS nano · February 2012 Graphite-coated, highly magnetic FeCo core-shell nanoparticles were synthesized by a chemical vapor deposition method and solubilized in aqueous solution through a unique polymer mixture modification, which significantly improved the biocompatibility and s ... Full text Cite

Near-infrared-fluorescence-enhanced molecular imaging of live cells on gold substrates.

Journal Article Angewandte Chemie (International ed. in English) · May 2011 Full text Cite

Deep-tissue anatomical imaging of mice using carbon nanotube fluorophores in the second near-infrared window.

Journal Article Proceedings of the National Academy of Sciences of the United States of America · May 2011 Fluorescent imaging in the second near-infrared window (NIR II, 1-1.4 μm) holds much promise due to minimal autofluorescence and tissue scattering. Here, using well-functionalized biocompatible single-walled carbon nanotubes (SWNTs) as NIR II fluorescent i ... Full text Cite

Optical properties of single-walled carbon nanotubes separated in a density gradient: Length, bundling, and aromatic stacking effects

Journal Article Journal of Physical Chemistry C · November 25, 2010 Single-walled carbon nanotubes (SWNTs) are promising materials for in vitro and in vivo biological applications due to their high surface area and inherent near-infrared photoluminescence and Raman scattering properties. Here, we use density gradient centr ... Full text Cite

Metal-enhanced fluorescence of carbon nanotubes.

Journal Article Journal of the American Chemical Society · November 2010 The photoluminescence (PL) quantum yield of single-walled carbon nanotubes (SWNTs) is relatively low, with various quenching effects by metallic species reported in the literature. Here, we report the first case of metal enhanced fluorescence (MEF) of surf ... Full text Cite

High performance in vivo near-IR (>1 μm) imaging and photothermal cancer therapy with carbon nanotubes

Journal Article Nano Research · January 1, 2010 Short single-walled carbon nanotubes (SWNTs) functionalized by PEGylated phospholipids are biologically non-toxic and long-circulating nanomaterials with intrinsic near infrared photoluminescence (NIR PL), characteristic Raman spectra, and strong optical a ... Full text Cite

A route to brightly fluorescent carbon nanotubes for near-infrared imaging in mice.

Journal Article Nature nanotechnology · November 2009 The near-infrared photoluminescence intrinsic to semiconducting single-walled carbon nanotubes is ideal for biological imaging owing to the low autofluorescence and deep tissue penetration in the near-infrared region beyond 1 microm. However, biocompatible ... Full text Cite

PEG branched polymer for functionalization of nanomaterials with ultralong blood circulation.

Journal Article Journal of the American Chemical Society · April 2009 Nanomaterials have been actively pursued for biological and medical applications in recent years. Here, we report the synthesis of several new poly(ethylene glycol) grafted branched polymers for functionalization of various nanomaterials including carbon n ... Full text Cite

Optical characterizations and electronic devices of nearly pure (10,5) single-walled carbon nanotubes.

Journal Article Journal of the American Chemical Society · February 2009 It remains an elusive goal to achieve high-performance single-walled carbon nanotube (SWNT) field-effect transistors (FETs) composed of only single-chirality SWNTs. Many separation mechanisms have been devised and various degrees of separation demonstrated ... Full text Cite

Carbon nanotubes in biology and medicine: In vitro and in vivo detection, imaging and drug delivery

Journal Article Nano Research · January 1, 2009 Carbon nanotubes exhibit many unique intrinsic physical and chemical properties and have been intensively explored for biological and biomedical applications in the past few years. In this comprehensive review, we summarize the main results from our and ot ... Full text Cite

Phospholipid-dextran with a single coupling point: a useful amphiphile for functionalization of nanomaterials.

Journal Article Journal of the American Chemical Society · January 2009 Nanomaterials hold much promise for biological applications, but they require appropriate functionalization to provide biocompatibility in biological environments. For noncovalent functionalization with biocompatible polymers, the polymer must also remain ... Full text Cite

Optical properties of ultrashort semiconducting single-walled carbon nanotube capsules down to sub-10 nm

Journal Article Journal of the American Chemical Society · May 21, 2008 Single-walled carbon nanotubes (SWNTs) are typically long (≳100 nm) and have been well established as novel quasi one-dimensional systems with interesting electrical, mechanical, and optical properties. Here, quasi zero-dimensional SWNTs with finite length ... Full text Cite

Selective probing and imaging of cells with single walled carbon nanotubes as near-infrared fluorescent molecules.

Journal Article Nano letters · February 2008 Fluorescent molecules emitting in the near-infrared (NIR, wavelength approximately 0.8-2 microm) are relatively scarce and have been actively sought for biological applications because cells and tissues exhibit little auto-fluorescence in this region. Here ... Full text Cite

Selective synthesis combined with chemical separation of single-walled carbon nanotubes for chirality selection

Journal Article Journal of the American Chemical Society · December 26, 2007 Single-walled carbon nanotubes (SWNTs) are potential materials for future nanoelectronics. Since the electronic and optical properties of SWNTs strongly depend on tube diameter and chirality, obtaining SWNTs with narrow (n,m) chirality distribution by sele ... Full text Cite