Hyperspectral coherent Raman scattering microscopy provides a significant improvement in acquisition time compared to spontaneous Raman scattering yet still suffers from the time required to sweep through individual wavenumbers. To address this, we present the use of a pulse shaper with a 2D spatial light modulator for phase- and amplitude-based shaping of the Stokes beam to create programmable spectrally tailored excitation envelopes. This enables collection of useful spectral information in a more rapid and efficient manner. © 2024 Optica Publishing Group.

Collagen is an essential component of biological tissues with a variety of subtypes. To be able to capture these subtypes, fully exploit the polarization-sensitive light-collagen interactions, and provide comprehensive information of collagen, we integrated polarization-sensitive second-harmonic generation (PSHG) microscopy, polarization-sensitive optical coherence microscopy (PSOCM), and two-photon fluorescence lifetime imaging microscopy into a single-source multimodal system in a simultaneous and spatially co-registered configuration. PSOCM information is used in the PSHG numerical model to enable accurate PSHG analysis of unsectioned fresh tissue. This polarization-sensitive multimodal system provides quantitative multiparametric characterization of collagen and facilitates the fundamental understanding of collagen in the unperturbed tissue microenvironment, which can enable future studies into the role of collagen in various diseases. © 2024 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement © 2024 Optica Publishing Group (formerly OSA). All rights reserved.

Multiphoton fluorescence lifetime imaging microscopy (FLIM) is used to collect label-free metabolic information from biological samples via autofluorescence lifetime imaging of reduced nicotinamide adenine dinucleotide and nicotinamide adenine dinucleotide phosphate (NAD(P)H). However, FLIM has traditionally been limited by slow acquisition due to the limited bandwidth of analog electronics that perform photon counting and time-tagging. This slow acquisition has restricted the applicability of multiphoton FLIM of NAD(P)H by impeding the ability to accurately study biological problems that require characterization of fast dynamics. Faster image acquisition can be achieved by directly digitizing the amplified output of a hybrid photodetector and computationally determining photon counts via the Single- and multiphoton PEak Event Detection (SPEED) algorithm. This method, bypassing the limited-bandwidth analog electronics used for photon counting and time-tagging of photons in traditional FLIM, enables fast photon counting capabilities which are well suited for fast, high-dynamic range biological processes such as metabolic changes during apoptosis. Here, we utilize this technology to examine fast dynamics of apoptosis in 2D culture of normal and cancerous human breast cell lines, rat mammary tumor tissue-derived organoids, and in vivo rat mammary tumors. Results indicate that apoptosis-related metabolic dynamics are biological model-dependent and based on local pharmacokinetics, with tumor derived organoids in Matrigel showing a significantly slower response than in vivo or in vitro 2D cell models. Future work should carefully consider these implications when determining which tumor model to use for experimentation and should improve tumor models to better represent in vivo tumor apoptosis dynamics. © 2023 SPIE.

Label-free optical imaging employs natural and non-destructive approaches to visualize biomedical samples for both biological assays and clinical diagnosis. At present, this field revolves around multiple technology-oriented communities, each with a specific focus on a particular modality, despite the existence of shared challenges and applications. As a result, biologists or clinical researchers who require label-free imaging are often not aware of the most appropriate modality to use. This Review presents a comprehensive overview of, and comparison among, different label-free imaging modalities and discusses common challenges and applications. We expect this Review to facilitate collaborative interactions between imaging communities, push the field forwards and foster technological advancements and biophysical discoveries, as well as facilitate new avenues in clinical detection, diagnosis and monitoring of diseases. © 2023, Springer Nature Limited.

Pancreatic cancer is a devastating disease often detected at later stages, necessitating swift and effective chemotherapy treatment. However, chemoresistance is common and its mechanisms are poorly understood. Here, label-free multi-modal nonlinear optical microscopy was applied to study microstructural and functional features of pancreatic tumors in vivo to monitor inter- and intra-tumor heterogeneity and treatment response. Patient-derived xenografts with human pancreatic ductal adenocarcinoma were implanted into mice and characterized over five weeks of intraperitoneal chemotherapy (FIRINOX or Gem/NabP) with known responsiveness/resistance. Resistant and responsive tumors exhibited a similar initial metabolic response, but by week 5 the resistant tumor deviated significantly from the responsive tumor, indicating that a representative response may take up to five weeks to appear. This biphasic metabolic response in a chemoresistant tumor reveals the possibility of intra-tumor spatiotemporal heterogeneity of drug responsiveness. These results, though limited by small sample size, suggest the possibility for further work characterizing chemoresistance mechanisms using nonlinear optical microscopy. © 2023. Springer Nature Limited.

Pseudomonas aeruginosa (P. aeruginosa) is a multidrug-resistant human pathogen involved in numerous infections. Understanding the response of P. aeruginosa to various treatments is critical to developing new ways for the antimicrobial susceptibly test and more effective treatment methods. Conventional antimicrobial susceptibility tests lack molecular information at the single bacterium level. In this study, we used label-free multimodal nonlinear optical microscopy to identify an autofluorescence signal from pyoverdine, a siderophore of the bacteria, for quantification of P. aeruginosa responses to antibiotics and blue light treatment. We also discovered that the bleaching of the pyoverdine autofluorescence signals is correlated with the inactivation of P. aeruginosa and is perhaps one of the mechanisms involved in the blue light inactivation of P. aeruginosa. © 2023 The Authors. Journal of Biophotonics published by Wiley-VCH GmbH.

Nonlinear optical imaging is a versatile tool that has been proven to be exceptionally useful in various research fields. However, due to the use of photomultiplier tubes (PMTs), the wide application of nonlinear optical imaging is limited by the incapability of imaging under ambient light. In this paper, we propose and demonstrate a new optical imaging detection method based on optical parametric amplification (OPA). As a nonlinear optical process, OPA intrinsically rejects ambient light photons by coherence gating. Periodical poled lithium niobate (PPLN) crystals are used in this study as the media for OPA. Compared to bulk nonlinear optical crystals, PPLN crystals support the generation of OPA signal with lower pump power. Therefore, this characteristic of PPLN crystals is particularly beneficial when using high-repetition-rate lasers, which facilitate high-speed optical signal detection, such as in spectroscopy and imaging. A PPLN-based OPA system was built to amplify the emitted imaging signal from second harmonic generation (SHG) and coherent anti-Stokes Raman scattering (CARS) microscopy imaging, and the amplified optical signal was strong enough to be detected by a biased photodiode under ordinary room light conditions. With OPA detection, ambient-light-on SHG and CARS imaging becomes possible, and achieves a similar result as PMT detection under strictly dark environments. These results demonstrate that OPA can be used as a substitute for PMTs in nonlinear optical imaging to adapt it to various applications with complex lighting conditions.

High-content screening (HCS) and high-throughput screening (HTS) are common processes used in biological research and drug discovery. They allow rapid examination of thousands of compounds tested at the same time for their activity in designed biological assays. After evolving in the 1990s, they quickly became pillars in the pharmaceutical industry, relying on the advances of process automation and adaptation of biochemical assays for small quantities, such as with multiple -well plates. The basic components of HTS and HCS are a miniaturized biological assay, automated transfers and liquid handling steps, and automated quantitative readouts of the assays. However, there has been an increased need for probing complex cellular and subcellular phenotypes as out-puts, such as changes in morphology and metabolic activity. The more common approach of labeling is expensive, time-consuming, and prohibits any usage of labeled cells or their products. Novel label-free noninvasive optical imaging could provide tools for multiparametric evaluation at the scale of biopharmaceutical production as well as for personalized medicine.

Significance: Needle biopsy (NB) procedures are important for the initial diagnosis of many types of cancer. However, the possibility of NB specimens being unable to provide diagnostic information, (i.e., non-diagnostic sampling) and the time-consuming histological evaluation process can cause delays in diagnoses that affect patient care.Aim: We aim to demonstrate the advantages of this label-free multimodal nonlinear optical imaging (NLOI) technique as a non-destructive point-of-procedure evaluation method for NB tissue cores, for the visualization and characterization of the tissue microenvironment.Approach: A portable, label-free, multimodal NLOI system combined second-harmonic generation (SHG) and third-harmonic generation and two- and three-photon autofluorescence (2PF, 3PF) microscopy. It was used for intraoperative imaging of fresh NB tissue cores acquired during canine cancer surgeries, which involved liver, lung, and mammary tumors as well as soft-tissue sarcoma; in total, eight canine patients were recruited. An added tissue culture chamber enabled the use of this NLOI system for longitudinal imaging of fresh NB tissue cores taken from an induced rat mammary tumor and healthy mouse livers.Results: The intraoperative NLOI system was used to assess fresh canine NB specimens during veterinary cancer surgeries. Histology-like morphological features were visualized by the combination of four NLOI modalities at the point-of-procedure. The NLOI results provided quantitative information on the tissue microenvironment such as the collagen fiber orientation using Fourier-domain SHG analysis and metabolic profiling by optical redox ratio (ORR) defined by 2PF/(2PF + 3PF). The analyses showed that the canine mammary tumor had more randomly oriented collagen fibers compared to the tumor margin, and hepatocarcinoma had a wider distribution of ORR with a lower mean value compared to the liver fibrosis and the normal-appearing liver. Moreover, the loss of metabolic information during tissue degradation of fresh murine NB specimens was shown by overall intensity decreases in all channels and an increase of mean ORR from 0.94 (standard deviation 0.099) to 0.97 (standard deviation 0.077) during 1-h longitudinal imaging of a rat mammary tumor NB specimen. The tissue response to staurosporine (STS), an apoptotic inducer, from fresh murine liver NB specimens was also observed. The mean ORR decreased from 0.86 to 0.74 in the first 40 min and then increased to 0.8 during the rest of the hour of imaging, compared to the imaging results without the addition of STS, which showed a continuous increase of ORR from 0.72 to 0.75.Conclusions: A label-free, multimodal NLOI platform reveals microstructural and metabolic information of the fresh NB cores during intraoperative cancer imaging. This system has been demonstrated on animal models to show its potential to provide a more comprehensive histological assessment and a better understanding of the unperturbed tumor microenvironment. Considering tissue degradation, or loss of viability upon fixation, this intraoperative NLOI system has the advantage of immediate assessment of freshly excised tissue specimens at the point of procedure. (C) The Authors. Published by SPIE under a Creative Commons Attribution 4.0 International License.