High speed unsupervised fluorescence lifetime imaging confocal multiwell plate reader for high content analysis

In vivo third-harmonic generation microscopy study on vitiligo patients

Melanin is known to provide strong third-harmonic generation (THG) contrast in human skin. With a high concentration in basal cell cytoplasm, THG contrast provided by melanin overshadows other THG sources in human skin studies. For better understanding of the THG signals in keratinocytes without the influence of melanin, an in vivo THG microscopy (THGM) study was first conducted on vitiliginous skin. As a result, the THG-brightness ratio between the melanin-lacking cytoplasm of basal cells and collagen fibers is about 1.106 at the dermal-epidermal junctions of vitiliginous skin, indicating high sensitivity of THGM for the presence of melanin. We further applied the in vivo THGM to assist evaluating the therapeutic outcome from the histopathological point of view for those showed no improvement under narrowband ultraviolet B therapy based on the seven-point Physician Global Assessment score. Our clinical study indicates the high potential of THGM to assist the histopathological assessment of the therapeutic efficacy of vitiligo treatments.

In vivo multiphoton kinetic imaging of the toxic effect of carbon tetrachloride on hepatobiliary metabolism

We used intravital multiphoton microscopy to study the recovery of hepatobiliary metabolism following carbon tetrachloride (CCl4) induced hepatotoxicity in mice. The acquired images were processed by a first order kinetic model to generate rate constant resolved images of the mouse liver. We found that with progression of hepatotoxicity, the spatial gradient of hepatic function disappeared. A CCl4-induced damage mechanism involves the compromise of membrane functions, resulting in accumulation of processed 6-carboxyfluorescein molecules. At day 14 following induction, a restoration of the mouse hepatobiliary function was found. Our approach allows the study of the response of hepatic functions to chemical agents in real time and is useful for studying pharmacokinetics of drug molecules through optical microscopic imaging.

Multiphoton autofluorescence lifetime imaging of induced pluripotent stem cells

The multiphoton fluorescence lifetime imaging tomograph MPTflex with its flexible 360-deg scan head, articulated arm, and tunable femtosecond laser source was employed to study induced pluripotent stem cell (iPS) cultures. Autofluorescence (AF) lifetime imaging was performed with 250-ps temporal resolution and submicron spatial resolution using time-correlated single-photon counting. The two-photon excited AF was based on the metabolic coenzymes NAD(P)H and flavin adenine dinucleotide/flavoproteins. iPS cells generated from mouse embryonic fibroblasts (MEFs) and cocultured with growth-arrested MEFs as feeder cells have been studied. Significant differences on AF lifetime signatures were identified between iPS and feeder cells as well as between their differentiating counterparts.

Reduced temporal sampling effect on accuracy of time-domain fluorescence lifetime Förster resonance energy transfer

Fluorescence lifetime imaging (FLIM) aims at quantifying the exponential decay rate of fluorophores to yield lifetime maps over the imaged sample. When combined with Förster resonance energy transfer (FRET), the technique can be used to indirectly sense interactions at the nanoscale such as protein–protein interactions, protein–DNA interactions, and protein conformational changes. In the case of FLIM-FRET, the fluorescence intensity decays are fitted to a biexponential model in order to estimate the lifetime and fractional amplitude coefficients of each component of the population of the donor fluorophore (quenched and nonquenched). Numerous time data points, also called temporal or time gates, are typically employed for accurately estimating the model parameters, leading to lengthy acquisition times and significant computational demands. This work investigates the effect of the number and location of time gates on model parameter estimation accuracy. A detailed model of a FLIM-FRET imaging system is used for the investigation, and the simulation outcomes are validated with in vitro and in vivo experimental data. In all cases investigated, it is found that 10 equally spaced time gates allow robust estimation of model-based parameters with accuracy similar to that of full temporal datasets (90 gates).

Quantitative changes in human epithelial cancers and osteogenesis imperfecta disease detected using nonlinear multicontrast microscopy

We show that combined multimodal nonlinear optical (NLO) microscopies, including two-photon excitation fluorescence, second-harmonic generation (SHG), third harmonic generation, and fluorescence lifetime imaging microscopy (FLIM) can be used to detect morphological and metabolic changes associated with stroma and epithelial transformation during the progression of cancer and osteogenesis imperfecta (OI) disease. NLO microscopes provide complementary information about tissue microstructure, showing distinctive patterns for different types of human breast cancer, mucinous ovarian tumors, and skin dermis of patients with OI. Using a set of scoring methods (anisotropy, correlation, uniformity, entropy, and lifetime components), we found significant differences in the content, distribution and organization of collagen fibrils in the stroma of breast and ovary as well as in the dermis of skin. We suggest that our results provide a framework for using NLO techniques as a clinical diagnostic tool for human cancer and OI. We further suggest that the SHG and FLIM metrics described could be applied to other connective or epithelial tissue disorders that are characterized by abnormal cells proliferation and collagen assembly.