A versatile optical microscope for time-dependent single-molecule and single-particle spectroscopy

Sorting Nanoparticles by Valency with DNA Barcoding

Self-assembly of DNA-labeled nanoparticles is an effective strategy to fabricate new nanocomposite materials and nanoscale devices from the bottom-up. To tailor the properties of the resulting material or device, one requires access to a wide range of nanoparticle sizes and shapes, as well as control over the number (valency) of DNA molecules on the nanoparticle surface. Currently, nanoparticles with a defined DNA valency can only be obtained in a narrow range of sizes, and in small quantities, limiting the properties of the resulting composite structures and their applications. Here, we leverage the digital information encoded in the number and sequence of short DNA barcodes to generate preparatory amounts of nanoparticles bearing a specific number of DNA molecules, irrespective of the identity of the nanocomponent. We show that this DNA valency sorting chromatography, which is driven by the selective affinity of Watson-Crick base pairs, is applicable to arbitrary DNA sequences and a broad range of nanoparticle sizes, shapes, and material compositions. To further demonstrate this fact, we use valency-sorted large gold nanospheres directly in self-assembly schemes to create, in one synthesis step, large amounts of several previously inaccessible molecule-like dimer and trimer nanostructures with unique optical properties. We anticipate that the expanded scope of DNA valency-defined nanoparticle reagents, and the increased scale at which they can be produced, will open new avenues for the molecularly precise manipulation of nanoscale matter.

A microwell array-based approach for studying single nanoparticle catalysis with high turnover frequency

Measuring the catalytical activities of single catalysts in the case of high turnover frequency (TOF, realistic conditions) is highly desirable to accurately evaluate the functional heterogeneities among individuals and to understand the catalytic mechanism. Herein, we report a microwell array-based method to in operando measure the photocatalytic kinetics of single CdS nanoparticles (NPs) with high TOF. This was realized by sealing individual CdS NPs into separated micrometer-sized polydimethylsiloxane wells, thus eliminating the diffusion of products among individuals in the case of high concentration of reactants. This method allowed us to monitor the activities of single catalysts with an average TOF up to 2.1 × 10⁵ s^-1. Interestingly, two types of catalytical behaviors were revealed during single CdS photocatalysis: a rapid decline in activity for most CdS NPs and an initial increase in activity followed by a decrease for a minor population of individuals. The developed method will facilitate the investigation of catalytic activities of single particles under realistic conditions and hold great potential in the fields of photo/electro-catalysts, enzymes, functional bacteria, and so on.

VIEW-MOD: a versatile illumination engine with a modular optical design for fluorescence microscopy

We developed VIEW-MOD (Versatile Illumination Engine with a Modular Optical Design): a compact, multi-modality microscope, which accommodates multiple illumination schemes including variable angle total internal reflection, point scanning and vertical/horizontal light sheet. This system allows combining and flexibly switching between different illuminations and imaging modes by employing three electrically tunable lenses and two fast-steering mirrors. This versatile optics design provides control of 6 degrees of freedom of the illumination source (3 translation, 2 tilt, and beam shape) plus the axial position of the imaging plane. We also developed standalone software with an easy-to-use GUI to calibrate and control the microscope. We demonstrate the applications of this system and software in biosensor imaging, optogenetics and fast 3D volume imaging. This system is ready to fit into complex imaging circumstances requiring precise control of illumination and detection paths, and has a broad scope of usability for a myriad of biological applications.

Preface: Special Topic on Single-Molecule Biophysics

Single-molecule measurements are now almost routinely used to study biological systems and processes. The scope of this special topic emphasizes the physics side of single-molecule observations, with the goal of highlighting new developments in physical techniques as well as conceptual insights that single-molecule measurements bring to biophysics. This issue also comprises recent advances in theoretical physical models of single-molecule phenomena, interpretation of single-molecule signals, and fundamental areas of statistical mechanics that are related to single-molecule observations. A particular goal is to illustrate the increasing synergy between theory, simulation, and experiment in single-molecule biophysics.

Optimal integration of wide field illumination and holographic optical tweezers for multimodal microscopy with ultimate flexibility and versatility

We introduce one-of-a-kind optical microscope that we have developed through optimized integration of wide-field and focused-light microscopies. This new instrument has accomplished operation of the same laser for both wide field illumination and holographic focused beam illumination interchangeably or simultaneously in a way scalable to multiple lasers. We have demonstrated its powerful capability by simultaneously carrying out Epi-fluorescence, total internal reflection fluorescence microscopy, selective plane illumination microscopy, and holographic optical tweezers with five lasers. Our instrument and the optical design will provide researchers across diverse fields, cell-biology and biophysics in particular, with a practical guidance to build an all-around multimodal microscope that will further inspire the development of novel hybrid microscopy experiments.