In this work, several optical-spectroscopic methods have been used to visualize and investigate the penetration of diamond nanoparticles (NPs) of various sizes (3–150 nm), surface structures and fluorescence properties into the animal skin in vitro. Murine skin samples have been treated with nanodiamond (ND) water suspensions and studied using optical coherence tomography (OCT), confocal and two-photon fluorescence microscopy and fluorescence lifetime imaging (FLIM). An analysis of the optical properties of the used nanodiamonds (NDs) enables the selection of optimal optical methods or their combination for the study of nanodiamond–skin interaction. Among studied NDs, particles of 100 nm in nominal size were shown to be appropriate for multimodal imaging using all three methods. All the applied NDs were able to cross the skin barrier and penetrate the different layers of the epidermis to finally arrive in the hair follicle niches. The results suggest that NDs have the potential for multifunctional applications utilizing multimodal imaging.

In this paper, optical measurement techniques, which enable non-invasive measurement, are superimposed to glucose sensing in scattering media. Used measurement techniques are Optical Coherence Tomography (OCT), Photoacoustic spectroscopy (PAS) and laser pulse Time-of-Flight (TOF) measurement using a streak camera. In parallel with measurements, a Monte-Carlo (MC) simulation models have been developed. Experimental in vitro measurements were performed using Intralipid fat emulsion as a tissue simulating phantom for OCT and TOF measurements. In PAS measurements, a pork meat was used as a subject but also preliminary in vivo measurements were done. OCT measurement results show that the slope of the OCT signal's envelope changes as a function of glucose content in the scattering media. TOF measurements show that the laser pulse full width of half maximum (FWHM) changes a little as function of glucose content. An agreement with MC-simulations and measurements with Intralipid was also found. Measurement results of PAS technique show that changes in glucose content in the pork meat tissue can be measured. In vivo measurements with a human volunteer show that other factors such as physiological change, blood circulation and body temperature drift may interfere the PA response of glucose.

In the present work, we report the imaging of Au nanostars nanoparticles (AuNSt) and their multifunctional applications in biomedical research and theranostics applications. Their optical and spectroscopic properties are considered for the multimodal imaging purpose. The AuNSt are prepared by the seed-meditated method and characterized for use as an agent for bio-imaging. To demonstrate imaging with AuNSt, penetration and localization in different biological models such as cancer cell culture (A549 lung carcinoma cell), 3D tissue model (multicellular tumor spheroid on the base of human oral squamous carcinoma cell, SAS) and murine skin tissue are studied. AuNSt were visualized using fluorescence lifetime imaging (FLIM) at two-photon excitation with a pulse duration 140 fs, repetition rate 80 MHz and 780 nm wavelength femtosecond laser. Strong emission of AuNSt at two-photon excitation in the near infrared range and fluorescence lifetime less than 0.5 ns were observed. It allows using AuNSt as a fluorescent marker at two-photon fluorescence microscopy and lifetime imaging (FLIM). It was shown that AuNSt can be observed inside a thick sample (tissue and its model). This is the first demonstration using AuNSt as an imaging agent for FLIM at two-photon excitation in biosystems. Increased scattering of near-infrared light upon excitation of AuNSt surface plasmon oscillation was also observed and rendered using a possible contrast agent for optical coherence tomography (OCT). AuNSt detection in a biological system using FLIM is compared with OCT on the model of AuNSt penetrating into animal skin. The AuNSt application for multimodal imaging is discussed.

Objective: This paper describes the full development of a sensor for measuring optical heart rate (OHR) and blood oxygen saturation (SpO₂). Methods: A wearable sensor with a new type of skin compatible dispensed lens was designed and manufactured. All critical optical components, light emitting diodes (LEDs) and photodiode (PD) were close to skin and gave maximum light intensity due to minimal loss in the lens structure. Lens and optical components formed a thin monolithic structure. Results: Suppressed crosstalk between LED and PD was achieved by using two types of dispensed material: light blocking and transparent. High signal to noise ratio (SNR) and amplitude in the alternating current (AC) part of the photoplethysmography (PPG) signal were achieved. User comfort was achieved by having a small sensor located on the upper arm. When re-training the algorithm from our first iteration, the multiwavelength PPG sensor showed an SpO₂ RMSE of 2.61% with a 7-second average analysis for 25 participants. The average RMSE of heart rate over all 25 participants was 1.6 ± 1.1%. Conclusion: This study demonstrates a sensor with a clinical grade SpO₂ measurement and a highly accurate OHR measurement that is also comfortable and easy to wear. Significance: A dispensing method provides a new way of manufacturing sensor elements for wearable sensors with increased performance with reduced crosstalk.

Background: Obstructive sleep apnea (OSA) affects over one billion people and increases neurodegenerative risk. Brain vasomotor, respiratory, and cardiac pulsations are thought to drive glymphatic clearance during sleep, yet OSA's effect on these pulsations remains poorly understood. Methods: We studied 20 healthy controls (HC; 39.7±8.0 y) and 12 patients with OSA (PWOSA; 53.0±11.0 y) using a four wavelength (690-980 nm) functional near-infrared spectroscopy (fNIRS) measuring oxygenated, deoxygenated and total hemoglobin, water and cerebrospinal fluid (HbO, HbR, HbT, H2O, CSF). Polar devices provided heart rate variability (HRV). Spectral power, coherence and phase transfer entropy analysis was performed for very low frequency (VLF), respiratory, and cardiac bands from 30 min sleep segments and event-based whole-night analysis assessed autonomic responses. Results: OSA patients exhibited lower fNIRS spectral entropy for HbO, HbT, H2O & CSF (p<0.05), with increased VLF and respiratory band power across all concentrations (HbO, HbR, HbT, H2O & CSF, p<0.05). Signal coherence was reduced in respiratory and cardiac bands. Phase transfer entropy revealed disrupted directional coupling toward HbR (cardiac) and CSF-to-HbO (respiratory). HRV showed parallel VLF amplification (p <0.05), elevated heart rate during event-free and respiratory-event periods (p<0.001) and reduced Root Mean Square of Successive Differences (RMSSD, 32.5 vs 43.0 ms, p0.73). Conclusions: OSA reorganizes cortical pulsatile dynamics – reducing complexity, amplifying low frequency power and disrupting directed coupling. This state may compromise sleep-related glymphatic clearance. fNIRS-based spectral analysis offers a promising bedside tool for monitoring brain pulsatility.