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The neutral nitrogen‐vacancy (NV0) defects in diamond are photostable color centers, suitable for a wide range of applications in science and engineering. However, the photophysical properties of the centers have not yet been fully characterized. This work measured the stimulated emission cross sections of NV0 in a single‐crystal diamond by two‐photon excitation of its matrix at 344 nm. From the measured photoluminescence spectrum and the fluorescence lifetime of 20 ± 1 ns, we determined a peak stimulated emission cross section of 1.43 ± 0.07 × 10−17 cm2 at 650 nm for the NV0 centers. In addition, we have also examined the thermal shifts of the zero‐phonon line of NV0 centers in nanoscale diamonds (~100 nm in diameter) over the temperature range of 30–120°C. A temperature measurement sensitivity of 0.2 K·Hz−1/2 was achieved, which is about two‐fold better than that of NV−, despite that the fluorescence intensity of NV0 is about six‐fold lower than that of NV− in the same nanoparticles. The result is attributed to the smaller electron–phonon coupling strength of the neutral center, compared with its negatively charged counterpart. [ABSTRACT FROM AUTHOR]

Lateral flow immunoassay (LFIA) is a widely used tool for point‐of‐care testing (POCT). Although the method is fast and inexpensive, it provides only qualitative or semi‐quantitative information, which limits the scope of its applications in POCT. Here, we report the development of a low‐cost, portable LFIA reader based on photothermal detection of reporters (such as colloidal gold and colored latex beads) captured on LFIA strips using a low‐power green laser as the heating source and a single‐element infrared sensor as the detector. For 40‐nm colloidal gold, we measured a detection limit of 3 × 105 particles/mm2 by laser irradiation of the reporters at 532 nm with an intensity of 20 W/cm2. The photothermal detection enables a 10‐fold enhancement in sensitivity over color visualization with the naked eye. More importantly, with the use of the control line intensities as internal calibrants, the results so obtained are quantitative and useful to support critical decision‐making in POCT, as demonstrated by gold‐based assays for human chorionic gonadotropin and human immunodeficiency virus as well as latex‐based assays for nucleocapsid protein of the SARS‐CoV‐2 virus. [ABSTRACT FROM AUTHOR]

Cathodoluminescence (CL) and correlative light‐electron microscopy (CLEM) are two useful analytical tools in diverse research areas. Recently, fluorescent nanodiamonds (FNDs) have emerged as promising imaging agents for both CL and CLEM owing to their exceptional photophysical and chemical properties. However, to realize their practical applications in the life sciences, surface modification and functionalization of the nanomaterials with bioactive molecules are critical and essential. Here we provide a comprehensive review on the methods of synthesizing biohybrid FNDs as well as recent advances of CL and CLEM imaging of cells with these carbon nanoparticles as dual‐contrast markers. [ABSTRACT FROM AUTHOR]

The first demonstration of nanodiamonds (NDs) for cellular fluorescence imaging was reported in 2005. It has since then aroused considerable interest among scientists working in the field of diamond and related materials. A large number of researches have been conducted, aimed to develop this novel nanomaterial as diagnostic, imaging, and therapeutic agents in biomedicine. There have been more than 20 review articles and book chapters published on this topic in the past 8 years. With the recent development of nanotechnologies and photonics, the ND-based bioimaging has been taken to a new level. In this topic review, we will focus our attention on the recent advances in the development of NDs as versatile bioimaging agents for both in vitro and in vivo applications. Emerging new technologies including multiphoton excitation imaging, superresolution imaging, optically detected magnetic resonance imaging, cathodoluminescence imaging, and photoacoustic imaging are discussed. [ABSTRACT FROM AUTHOR]

Denaturation of oxidized cytochrome c (cyt c) adsorbed to a hydrophilic fused silica surface was studied by UV-VIS attenuated total reflection (ATR) spectroscopy using a multiple optical pass system newly developed by this lab. Cyt c surface adsorption at neutral pH gave an adsorption equilibrium constant of Ka = 2 × 105 M−1 and a surface coverage at 63% of a monolayer saturation. Protein unfolding by acid denaturation was studied by equilibrating surface bound cyt c with acid buffers ranging in pH from 5 to 2. Protein orientation and surface coverage were calculated based on a theoretical model developed in previous work. The average heme tilt angle (44°) was found to be independent of pH, implicating protein-surface interactions as the dominant factor governing adsorption. A non-random molecular orientation distribution of cyt c on the surface was observed, providing further support for the dominance of protein-surface interactions. It was shown that when denaturing acid buffers were removed and replaced with a neutral buffer cyt c refolded, assuming their original conformation. The combination of unique, yet applicable, science and laboratory skills involved in this project had a tremendous impact on the authors' undergraduate curriculum, making it ideal for capstone project development. [ABSTRACT FROM AUTHOR]