Among plasmonic applications, photoacoustic (PA) generation stands out due to the emergence of nanoparticle mediated PA imaging in recent years [1]. For metallic nanoparticle mediated PA excitation, thermal effects are crucial contributors to the production of pressure waves. However, the fraction of heat converted into mechanical work has dependency on both the thermophysical constants of the medium and the nanoparticle. In this work, we investigate the effect of optimized metallic nanospheres in PA generation by nanosecond laser pulses (7ns, 10Hz) for sizes 5, 50 and 100nm at 530nm laser excitation. The results are in accordance with the theoretical prediction, based on the analysis of the NP temperature rise.

Fluorescence-based imaging is a powerful tool for studying biological systems, but its application in vivo is hindered by tissue scattering and autofluorescence. To enhance the usefulness of non-invasive in vivo fluorescence imaging, a comprehensive understanding of these factors is crucial. This presentation introduces a diffusion model that represents a fluorophore within tissue, verified using Monte Carlo simulations and experimental measurements with tissue-like phantom slabs of varying reduced scattering coefficients and thicknesses. The study reveals a correlation between fluorescence intensity (FI) and thickness, confirming the expected decay. Surprisingly, the exponential decay rate decreases with increasing scattering coefficient, contradicting intuition. This counterintuitive finding suggests that highly scattering media result in weaker FI decay dependence on tissue depth, reducing fluorescence artifacts from deeper regions.

Liquid biopsy promises non-invasive collection and characterization of diagnostic-relevant samples, with small extracellular vesicles (exosomes) playing an increasingly important role. While surface molecular markers are often used to select and analyze exosomes with specific disease characteristics, label-free methodologies have been developed, with the benefit of single exosome analysis that may uncover exosome heterogeneity and its role in pathology. We present examples of Raman and SERS for single exosome characterization, highlighting strategies for exosome capturing, signal collection, and data analysis. In addition, we discuss limitations, with emphasis on capturing, where very few pathology-relevant exosomes are available for analysis.

The presence of natural fluorescence in cellular structures and the use of fluorescent probes enables in vivo monitoring of biological and biophysical phenomena with high sensitivity and selectivity. In recent years, the development of on-chip lensless platforms has enabled the development of compact imaging devices. In this work we implement fluorescence detection on a contact, lensless CMOS-based image platform exploring a total internal reflection fluorescence configuration. Our fluorescent imaging platform has the potential to achieve micrometer-scale spatial resolution with a Field of View determined by the size of the semiconductor sensor (in our case 3.68mm x 2.76mm).

Nano-CET (Dispertech) was used to determine the refractive index (RI) of extracellular vesicles (EVs)<100 nm, as it simultaneously measures the trajectory and scattering intensity of particles within a nanofluidic optical fiber. A test sample of outdated erythrocyte-derived EVs was developed for RI determination. Polystyrene beads and silica beads of known sizes were used for calibration and validation. A Python algorithm was developed to track the position and scattering intensity of single particles. The determined RIs of silica beads and hollow organosilica beads (HOBs) matched literature values. Measured RI of EVs was higher (1.63±0.06) than anticipated (RI~1.48), perhaps due to an elevated hemoglobin concentration in outdated erythrocyte EVs.

There is great attention on the development of quick, easy, and sensitive detection techniques for cancer biomarkers. Surface-enhanced Raman spectroscopy (SERS) is a powerful analytical technique that has gained significant attention in the field of cancer research. SERS-based immunoassays are often utilized for the detection of biological structures and molecules in medicine. In the study, a SERS-based immunosensor is developed for the detection of cancer protein biomarkers in serum on a flexible diatomite-based SERS active platform. The flexible SERS active platform is prepared on a regular box tape by coating nanoporous biosilica (diatomite) with AgNPs using the layer-by-layer assembly method. The platform is then modified with antibodies specific to target cancer proteins, such as human epidermal growth factor receptor2 (HER2), mucin4 (MUC 4), and prostate-specific antigen (PSA). The antibody-modified surface is incubated with the cancer proteins spiked in serum at different concentrations, and SERS spectra are obtained after the incubation of Raman probes. The method's sensitivity is evaluated, and the capability to detect protein biomarkers down to 0.1 ng/mL is demonstrated.

SCOBY is a biomaterial derived from a symbiotic culture of bacteria and yeast. Its structure is characterized by intercalated nanocellulose fibers. There has been increased interest in using this bacterial nanocellulose to medical applications and in biosensors. For successful applications, their mechanical, optical, and electrical properties need to be characterized and improved. We report experimental results on the optical absorption, emission, and scattering properties of SCOBY and derivations of SCOBY. In addition, we demonstrate improved electrical conductivity by the addition of PEDOT:PSS and AgNPs into the nanocellulose matrix, leading to the possibility of SERS and luminescence emission for nanoscale biosensing applications.

Through applications of fluorescence correlation spectroscopy, our research has provided a unique view of HIV virion-antibody interactions. We developed a novel FRET-FCS based assay to identify how neutralizing and non-neutralizing epitopes are expressed on single virions. Most of our methods can be expanded for application to studies of in vitro primary infection systems. Recently, we developed a quantitative, intrinsic, label-free, and minimally invasive method based on two-photon fluorescence lifetime (FLT) imaging microscopy (2p-FLIM) for imaging NADH metabolism of virally infected cells and tissue sections.

A novel on-chip chemiluminescence biosensor is developed to assess cleanliness of the solid surfaces. The sensor is based on ATP-mediated chemiluminescence detection. It provides high-sensitivity detection of surface contamination due to improved photon collection efficiency. The results show the dependence of the bioluminescence enhancement on ATP concentration. We report the limit of detection of the biosensor. We demonstrate the use of the biosensor for real sample analysis to assess surface contamination of the laboratory and office equipment. This suggests the use of the biosensor in practical applications such as the food processing industry, laboratory environments, and health care settings.

Single-photon avalanche diode (SPAD) arrays have surpassed other detector technologies ; photon-multiplying tubes (PMTs) in signal-noise ratio (SNR) and electron multiplied charge coupled devices (EMCCDs) in frame rate andphoton fidelity, and have proven beneficial for advanced microscopy applications. Resolution and SNR improvements have been demonstrated in image scanning microscopy (ISM) and quantum image scanning microscopy (qISM) . Despite SPAD arrays reaching near 100% fill factor thanks to optimized micro lense design and fabrication processes, the photon detection efficiency (PDE) remains limited in the red and near-IR wavelengths. In this work, we present a 23-channels SPAD array with low dark count rate (DCR), picosecond time tagging capabilities and improved sensitivity for wavelength from 600 to 1000 nm. The fabrication process is fully CMOS compatible and easily scalable to larger arrays. We show a PDE of 60% and 15% at 620 nm and 900 nm, respectively. Despite the increased spectral response, the SPAD array keeps a very low ambient temperature DCR of less than 100 counts per second.