Novel Nanocomposites for Luminescent Thermometry with Two Different Modalities.

In this work, we successfully integrated fluorescent nanodiamonds (FNDs) and lanthanide ion-doped upconversion nanoparticles (UCNPs) in a nanocomposite structure for simultaneous optical temperature sensing. The effective integration of FND and UCNP shells was confirmed by employing high-resolution TEM imaging, X-ray diffraction, and dual-excitation optical spectroscopy. Furthermore, the synthesized ND@UCNP nanocomposites were tested by making simultaneous optical temperature measurements, and the detected temperatures showed excellent agreement within their sensitivity limit. The simultaneous measurement of temperature using two different modalities having different sensing physics but with the same composite nanoparticles inside is expected to greatly improve the confidence of nanoscale temperature measurements. This should resolve some of the controversy surrounding nanoscale temperature measurements in biological applications.

A Novel Non-Destructive Rapid Tool for Estimating Amino Acid Composition and Secondary Structures of Proteins in Solution.

Amino-acid protein composition plays an important role in biology, medicine, and nutrition. Here, a groundbreaking protein analysis technique that quickly estimates amino acid composition and secondary structure across various protein sizes, while maintaining their natural states is introduced and validated. This method combines multivariate statistics and the thermostable Raman interaction profiling (TRIP) technique, eliminating the need for complex preparations. In order to validate the approach, the Raman spectra are constructed of seven proteins of varying sizes by utilizing their amino acid frequencies and the Raman spectra of individual amino acids. These constructed spectra exhibit a close resemblance to the actual measured Raman spectra. Specific vibrational modes tied to free amino and carboxyl termini of the amino acids disappear as signals linked to secondary structures emerged under TRIP conditions. Furthermore, the technique is used inversely to successfully estimate amino acid compositions and secondary structures of unknown proteins across a range of sizes, achieving impressive accuracy ranging between 1.47% and 5.77% of root mean square errors (RMSE). These results extend the uses for TRIP beyond interaction profiling, to probe amino acid composition and structure.

Optical multiband polarimetric modulation sensing for gender and species identification of flying native solitary pollinators.

Native pollinators are crucial to local ecosystems but are under threat with the introduction of managed pollinators, e.g., honeybees (Apis mellifera). We explored the feasibility of employing the entomological lidar technique in native pollinator abundance studies. This study included individuals of both genders of three common solitary bee species, Osmia californica, Osmia lignaria, and Osmia ribifloris, native to North America. Properties including optical cross-section, degree of linear polarization, and wingbeat power spectra at all three wavelengths have been extracted from the insect signals collected by a compact stand-off sensing system. These properties are then used in the classification analysis. For species with temporal and spatial overlapping, the highest accuracies of our method exceed 96% (O. ribifloris & O. lignaria) and 93% (O. lignaria & O. californica). The benefit of employing the seasonal activity and foraging preference information in enhancing identification accuracy has been emphasized.

Label-free drug interaction screening via Raman microscopy.

Development of a simple, label-free screening technique capable of precisely and directly sensing interaction-in-solution over a size range from small molecules to large proteins such as antibodies could offer an important tool for researchers and pharmaceutical companies in the field of drug development. In this work, we present a thermostable Raman interaction profiling (TRIP) technique that facilitates low-concentration and low-dose screening of binding between protein and ligand in physiologically relevant conditions. TRIP was applied to eight protein-ligand systems, and produced reproducible high-resolution Raman measurements, which were analyzed by principal component analysis. TRIP was able to resolve time-depending binding between 2,4-dinitrophenol and transthyretin, and analyze biologically relevant SARS-CoV-2 spike-antibody interactions. Mixtures of the spike receptor-binding domain with neutralizing, nonbinding, or binding but nonneutralizing antibodies revealed distinct and reproducible Raman signals. TRIP holds promise for the future developments of high-throughput drug screening and real-time binding measurements between protein and drug.

Electrodeposition of Lithium-Based Upconversion Nanoparticle Thin Films for Efficient Perovskite Solar Cells.

In this work, high-quality lithium-based, LiYF4=Yb3+,Er3+ upconversion (UC) thin film was electrodeposited on fluorene-doped tin oxide (FTO) glass for solar cell applications. A complete perovskite solar cell (PSC) was fabricated on top of the FTO glass coated with UC thin film and named (UC-PSC device). The fabricated UC-PSC device demonstrated a higher power conversion efficiency (PCE) of 19.1%, an additional photocurrent, and a better fill factor (FF) of 76% in comparison to the pristine PSC device (PCE = ~16.57%; FF = 71%). Furthermore, the photovoltaic performance of the UC-PSC device was then tested under concentrated sunlight with a power conversion efficiency (PCE) of 24% without cooling system complexity. The reported results open the door toward efficient PSCs for renewable and green energy applications.

Lightly Boron-Doped Nanodiamonds for Quantum Sensing Applications.

Unlike standard nanodiamonds (NDs), boron-doped nanodiamonds (BNDs) have shown great potential in heating a local environment, such as tumor cells, when excited with NIR lasers (808 nm). This advantage makes BNDs of special interest for hyperthermia and thermoablation therapy. In this study, we demonstrate that the negatively charged color center (NV) in lightly boron-doped nanodiamonds (BNDs) can optically sense small temperature changes when heated with an 800 nm laser even though the correct charge state of the NV is not expected to be as stable in a boron-doped diamond. The reported BNDs can sense temperature changes over the biological temperature range with a sensitivity reaching 250 mK/√Hz. These results suggest that BNDs are promising dual-function bio-probes in hyperthermia or thermoablation therapy as well as other quantum sensing applications, including magnetic sensing.

Quantum optical immunoassay: upconversion nanoparticle-based neutralizing assay for COVID-19.

In a viral pandemic, a few important tests are required for successful containment of the virus and reduction in severity of the infection. Among those tests, a test for the neutralizing ability of an antibody is crucial for assessment of population immunity gained through vaccination, and to test therapeutic value of antibodies made to counter the infections. Here, we report a sensitive technique to detect the relative neutralizing strength of various antibodies against the SARS-CoV-2 virus. We used bright, photostable, background-free, fluorescent upconversion nanoparticles conjugated with SARS-CoV-2 receptor binding domain as a phantom virion. A glass bottom plate coated with angiotensin-converting enzyme 2 (ACE-2) protein imitates the target cells. When no neutralizing IgG antibody was present in the sample, the particles would bind to the ACE-2 with high affinity. In contrast, a neutralizing antibody can prevent particle attachment to the ACE-2-coated substrate. A prototype system consisting of a custom-made confocal microscope was used to quantify particle attachment to the substrate. The sensitivity of this assay can reach 4.0 ng/ml and the dynamic range is from 1.0 ng/ml to 3.2 [Formula: see text]g/ml. This is to be compared to 19 ng/ml sensitivity of commercially available kits.

Dynamic nitrogen vacancy magnetometry by single-shot optical streaking microscopy.

Nitrogen vacancy diamonds have emerged as sensitive solid-state magnetic field sensors capable of producing diffraction limited and sub-diffraction field images. Here, for the first time, to our knowledge, we extend those measurements to high-speed imaging, which can be readily applied to analyze currents and magnetic field dynamics in circuits on a microscopic scale. To overcome detector acquisition rate limitations, we designed an optical streaking nitrogen vacancy microscope to acquire two-dimensional spatiotemporal kymograms. We demonstrate magnetic field wave imaging with micro-scale spatial extent and ~400 µs temporal resolution. In validating this system, we detected magnetic fields down to 10 µT for 40 Hz magnetic fields using single-shot imaging and captured the spatial transit of an electromagnetic needle at streak rates as high as 110 µm/ms. This design has the capability to be readily extended to full 3D video acquisition by utilizing compressed sensing techniques and a potential for further improvement of spatial resolution, acquisition speed, and sensitivity. The device opens opportunities to many potential applications where transient magnetic events can be isolated to a single spatial axis, such as acquiring spatially propagating action potentials for brain imaging and remotely interrogating integrated circuits.

Lithium-Based Upconversion Nanoparticles for High Performance Perovskite Solar Cells.

In this work, we report an easy, efficient method to synthesize high quality lithium-based upconversion nanoparticles (UCNPs) which combine two promising materials (UCNPs and lithium ions) known to enhance the photovoltaic performance of perovskite solar cells (PSCs). Incorporating the synthesized YLiF4:Yb,Er nanoparticles into the mesoporous layer of the PSCs cells, at a certain doping level, demonstrated a higher power conversion efficiency (PCE) of 19%, additional photocurrent, and a better fill factor (FF) of 82% in comparison to undoped PSCs (PCE = ~16.5%; FF = 71%). The reported results open a new avenue toward efficient PSCs for renewable energy applications.

Quantum Optical Immunoassay: Upconversion Nanoparticle-based Neutralizing Assay for COVID-19.

In a viral pandemic, a few important tests are required for successful containment of the virus and reduction in severity of the infection. Among those tests, a test for the neutralizing ability of an antibody is crucial for assessment of population immunity gained through vaccination, and to test therapeutic value of antibodies made to counter the infections. Here, we report a sensitive technique to detect the relative neutralizing strength of various antibodies against the SARS-CoV-2 virus. We used bright, photostable, background-free, fluorescent upconversion nanoparticles conjugated with SARS-CoV-2 receptor binding domain as a phantom virion. A glass bottom plate coated with angiotensin-converting enzyme 2 (ACE-2) protein imitates the target cells. When no neutralizing IgG antibody was present in the sample, the particles would bind to the ACE-2 with high affinity. In contrast, a neutralizing antibody can prevent particle attachment to the ACE-2-coated substrate. A prototype system consisting of a custom-made confocal microscope was used to quantify particle attachment to the substrate. The sensitivity of this assay can reach 4.0 ng/ml and the dynamic range is from 1.0 ng/ml to 3.2 {\mu}g/ml. This is to be compared to 19 ng/ml sensitivity of commercially available kits.

Raman Spectroscopy as a Robust New Tool for Rapid and Accurate Evaluation of Drought Tolerance Levels in Both Genetically Diverse and Near-Isogenic Maize Lines.

Improving drought tolerance of crops has become crucial due to the current scenario of rapid climate change. In particular, development of new maize germplasm with increased drought tolerance is viewed as a major breeding goal to ensure sustainable food and feed production. Therefore, accurate rapid phenotyping techniques for selection of superior maize genotypes are required. The objectives of this study were to determine whether Raman microscopy technique can be applied for accurate assessment of drought-tolerance levels in both genetically diverse and near-isogenic maize lines that differ in their levels of drought-tolerance. Carotenoid degradation is known to be a direct stress response initiated by reactive oxygen species during osmotic stress such as drought. Using Raman mapping, we observed real-time changes in the rate of carotenoid degradation in chloroplasts that was dependent on the strength of osmotic stress. In addition, we showed that the rate of carotenoid degradation as measured by Raman spectroscopy correlates directly with drought tolerance levels of diverse maize genotypes. We conclude that Raman technique is a robust, biochemically selective and non-invasive phenotyping technique that accurately distinguishes drought tolerance levels in both genetically diverse and near-isogenic maize genotypes. We conclude that this technique can be further developed to render it suitable for field-based early assessment of breeding materials with superior drought-tolerance traits.

Photostable and Small YVO4:Yb,Er Upconversion Nanoparticles in Water.

In this work, we report a simple method of silica coating of upconversion nanoparticles (UCNPs) to obtain well-crystalline particles that remain small and not agglomerated after high-temperature post-annealing, and produce bright visible emission when pumped with near-infrared light. This enables many interesting biological applications, including high-contrast and deep tissue imaging, quantum sensing and super-resolution microscopy. These VO4-based UNCPs are an attractive alternative to fluoride-based crystals for water-based biosensing applications.

Engineering Red-Enhanced and Biocompatible Upconversion Nanoparticles.

The exceptional optical properties of lanthanide-doped upconversion nanoparticles (UCNPs) make them among the best fluorescent markers for many promising bioapplications. To fully utilize the unique advantages of the UCNPs for bioapplications, recent significant efforts have been put into improving the brightness of small UCNPs crystals by optimizing dopant concentrations and utilizing the addition of inert shells to avoid surface quenching effects. In this work, we engineered bright and small size upconversion nanoparticles in a core-shell-shell (CSS) structure. The emission of the synthesized CSS UCNPs is enhanced in the biological transparency window under biocompatible excitation wavelength by optimizing dopant ion concentrations. We also investigated the biosafety of the synthesized CSS UCNP particles in living cell models to ensure bright and non-toxic fluorescent probes for promising bioapplications.

Extended focal depth Fourier domain optical coherence microscopy with a Bessel-beam - LP02 mode - from a higher order mode fiber.

We present a robust fiber-based setup for Bessel-like beam extended depth-of-focus Fourier-domain optical coherence microscopy, where the Bessel-like beam is generated in a higher order mode fiber module. In this module a stable guided LP02 core mode is selectively excited by a long period grating written in the higher order mode fiber. Imaging performance of this system in terms of lateral resolution and depth of focus was analyzed using samples of suspended microbeads and compared to the case where illumination is provided by the fundamental LP01 mode of a single mode fiber. Illumination with the LP02 mode allowed for a lateral resolution down to 2.5 µm as compared to 4.5 µm achieved with the LP01 mode of the single mode fiber. A three-fold enhancement of the depth of focus compared to a Gaussian beam with equally tight focus is achieved with the LP02 mode. Analysis of the theoretical lateral point spread functions for the case of LP01 and LP02 illumination agrees well with the experimental data. As the design space of waveguides and long-period gratings allows for further optimization of the beam parameters of the generated Bessel-like beams in an all-fiber module, this approach offers a robust and yet flexible alternative to free-space optics approaches or the use of conical fiber tips.

Enhancing sensitivity of lateral flow assay with application to SARS-CoV-2.

Lateral flow assay (LFA) has long been used as a biomarker detection technique. It has advantages such as low cost, rapid readout, portability, and ease of use. However, its qualitative readout process and lack of sensitivity are limiting factors. We report a photon-counting approach to accurately quantify LFAs while enhancing sensitivity. In particular, we demonstrate that the density of SARS-CoV-2 antibodies can be quantified and measured with an enhanced sensitivity using this simple laser optical analysis.

Engineering of Shallow Layers of Nitrogen Vacancy Colour Centres in Diamond Using Plasma Immersion Ion Implantation.

Sensing nano-scale magnetic field sources is at the heart of many applications in nano-science and biology. Given its very small size and high magnetic sensitivity, the nitrogen vacancy (NV) colour centre in diamond is one of the leading candidates for such applications. However, issues regarding the stability and performance of the NV centre near the diamond's surface are the major obstacle in the practical realization of theses sensors. So far, conventional implantation and growth techniques did not produce practical and/or repeatable solutions to this problem. In this report, we show first results of shallow layers of NVs created using plasma immersion ion implantation (PIII). We show, using Forster Resonance Energy Transfer (FRET), that most NVs are within 3.6 nm from the diamond's surface. Despite the relatively low quality of the diamond substrates used and the simplicity of our PIII system, we have an estimated magnetic sensitivity of around 2.29 µT/[Formula: see text].

Fluorescent nanodiamonds for luminescent thermometry in the biological transparency window.

Fluorescent nanodiamonds (FNDs) have attracted recent interest for biological applications owing to their biocompatibility and photostability (absence of photoblinking and bleaching). For optical thermometry, nitrogen-vacancy (NV) color centers and silicon-vacancy color centers in diamonds have demonstrated potential, where the NV has the highest sensitivity. However, NV is often excited with green light, which can cause heating and photodamage to tissues, as well as autofluorescence that decreases sensitivity. To overcome these limitations, we report temperature sensing using NV centers excited by deep red light (660 nm), plus another color center that can be excited with NIR light; the nickel (Ni) complex. The NV center measures temperature using diamond lattice expansion while the Ni complex measures temperature using phonon sideband strength.

Fluorescent nanodiamond-bacteriophage conjugates maintain host specificity.

Rapid identification of specific bacterial strains within clinical, environmental, and food samples can facilitate the prevention and treatment of disease. Fluorescent nanodiamonds (FNDs) are being developed as biomarkers in biology and medicine, due to their excellent imaging properties, ability to accept surface modifications, and lack of toxicity. Bacteriophages, the viruses of bacteria, can have exquisite specificity for certain hosts. We propose to exploit the properties of FNDs and phages to develop phages conjugated with FNDs as long-lived fluorescent diagnostic reagents. In this study, we develop a simple procedure to create such fluorescent probes by functionalizing the FNDs and phages with streptavidin and biotin, respectively. We find that the FND-phage conjugates retain the favorable characteristics of the individual components and can discern their proper host within a mixture. This technology may be further explored using different phage/bacteria systems, different FND color centers and alternate chemical labeling schemes for additional means of bacterial identification and new single-cell/virus studies.

Nanometer-scale luminescent thermometry in bovine embryos.

Luminescent nanothermometry is a powerful tool that can precisely monitor temperature changes in animal embryos. Among the most sensitive nanoluminescent temperature sensors are fluorescent nanodiamonds (FNDs), having nitrogen-vacancy color centers, and lanthanide-ion-doped upconversion nanoparticles (UCNPs). Here, we investigate their use as nanothermometers inside bovine embryos. The motivation for using both FNDs and UCNPs to measure temperature is to avoid the question of sensor confusion by the local cellular environment. Specifically, by simultaneously measuring temperature using two different modalities having different physics, it is possible to greatly improve the measurement confidence, thereby directly addressing the recent controversy surrounding temperature measurements in living organisms.