# Multispectral Laser‐Scanning Photoacoustic Microscopy With SRS‐Generated Wavelengths for Skin Chromophore Characterization

## TL;DR

A new imaging system uses laser scanning and Raman scattering to visualize skin components like hemoglobin, melanin, and collagen without dyes.

## Contribution

A compact, single-source multispectral photoacoustic microscopy system with SRS-based wavelength generation for label-free skin chromophore imaging.

## Key findings

- The system enables precise spectral discrimination of oxyhemoglobin, deoxyhemoglobin, melanin, and collagen in mouse skin.
- In vivo experiments showed accurate chromophore separation and spatially resolved oxygen saturation mapping.
- The method allows visualization of collagen and melanin architectures in pigmented and melanin-deficient mouse models.

## Abstract

We present a single pump‐source, multispectral laser‐scanning photoacoustic microscopy (MS‐LS‐PAM) platform that integrates stimulated Raman scattering (SRS)‐based wavelength generation for high‐resolution, label‐free skin imaging. The system uses a compact, fiber‐based light source to produce tunable excitation wavelengths from 532 to 571 nm, enabling precise spectral discrimination of key endogenous chromophores, oxyhemoglobin (HbO2), deoxyhemoglobin (Hb), melanin, and collagen, without external contrast agents. Spectral unmixing is performed using non‐negative least squares (NNLS), facilitating quantitative analysis of chromophore distributions. In vivo experiments on B6 (pigmented) and SKH1 hairless (melanin deficient) mice demonstrated accurate chromophore separation, spatially resolved oxygen saturation (sO2) mapping, and clear visualization of collagen and melanin architectures.

Unmixed maps showing vascular oxygen saturation (sO2), relative collagen, and relative melanin distributions. Maps were extracted from multispectral imaging of B6 and SKH1 Nude mouse abdominal skin using the proposed MS‐LS‐PAM system.