Automated label-free detection of injured neuron with deep learning by two-photon microscopy.

Stroke is a significant cause of morbidity and long-term disability globally. Detection of injured neuron is a prerequisite for defining the degree of focal ischemic brain injury, which can be used to guide further therapy. Here, we demonstrate the capability of two-photon microscopy (TPM) to label-freely identify injured neurons on unstained thin section and fresh tissue of rat cerebral ischemia-reperfusion model, revealing definite diagnostic features compared with conventional staining images. Moreover, a deep learning model based on convolutional neural network is developed to automatically detect the location of injured neurons on TPM images. We then apply deep learning-assisted TPM to evaluate the ischemic regions based on tissue edema, two-photon excited fluorescence signal intensity, as well as neuronal injury, presenting a novel manner for identifying the infarct core, peri-infarct area, and remote area. These results propose an automated and label-free method that could provide supplementary information to augment the diagnostic accuracy, as well as hold the potential to be used as an intravital diagnostic tool for evaluating the effectiveness of drug interventions and predicting potential therapeutics.

Label-free multiphoton imaging of ß-amyloid plaques in Alzheimer's disease mouse models.

ß -Amyloid ( A ß ) plaque, representing the progressive accumulation of the protein that mainly consists of A ß , is one of the prominent pathological hallmarks of Alzheimer's disease (AD). Label-free imaging of A ß plaques holds the potential to be a histological examination tool for diagnosing AD. We applied label-free multiphoton microscopy to identify extracellular A ß plaque as well as intracellular A ß accumulation for the first time from AD mouse models. We showed that a two-photon-excited fluorescence signal is a sensitive optical marker for revealing the spatial-temporal progression and the surrounding morphological changes of A ß deposition, which demonstrated that both extracellular and intracellular A ß accumulations play an important role in the progression of AD. Moreover, combined with a custom-developed image-processing program, we established a rapid method to visualize different degrees of A ß deposition by color coding. These results provide an approach for investigating pathophysiology of AD that can complement traditional biomedical procedures.

Polarization-independent Fabry-Perot interferometer in a hole-type silicon photonic crystal.

We propose and numerically demonstrate a polarization-independent Fabry-Perot interferometer (PI-FPI) based on the self-collimation effect in a hole-type silicon photonic crystal (PhC). By use of the polarization peak matching method, a resonance frequency of the transverse-electric modes can equal that of the transverse-magnetic modes in the PI-FPI, although the transmission spectra are quite polarization dependent due to birefringence of the PhC. For the operating wavelength of 1550 nm, the PI free spectral range of the PI-FPI is up to 32.3 nm, which nearly covers the whole optical communication C-band window. With its small dimensions, simple structure, and silicon-based material, this PI-FPI may play an important role in photonic integrated circuits.