Nuriya, M. | Search bioRxiv

bioRxiv2026

Correlation-resolved sum-frequency generation microscopy of biological tissue with bright twin beams

Sum-frequency generation (SFG) driven by bright twin beams generated through high-gain parametric down-conversion comprises a coherent component arising from correlated mode pairs and an incoherent component arising from interactions between uncorrelated modes. Modal correlations can enhance coherent SFG in anisotropic nonlinear media, for example by extending the effective interaction length. Whether such correlations can likewise benefit image formation in heterogeneous biological tissue remains unknown. Here we address this question by performing SFG imaging of biological tissue using bright twin beams as the excitation source. Spectral decomposition of the SFG signal separates its coherent and incoherent components, allowing us to reconstruct co-registered images and examine how twin-beam correlations influence image formation. In mouse skeletal muscle, the coherent-component image revealed sarcomere periodicity with a Bragg-spot-to-background ratio of approximately 310, compared with 7.5 in the incoherent-component image. In fresh human dermis, the coherent-component image showed greater Fourier power than the incoherent-component image in the 0.30-0.50 \mu m^{-1} band and a greater fractional autocovariance decay at short spatial lags. These results demonstrate that twin-beam correlations can enhance contrast and detectability at selected spatial frequencies in heterogeneous tissue. Correlation-resolved SFG microscopy thus offers a route for exploiting bright quantum-light sources in nonlinear optical bioimaging.

biophysics↗

bioRxiv2024

Label-free visualization of ciliary rootlets in mouse brain

Neuronal primary cilia are important role in brain development, sensory perception and neurogenesis. Rootletin, a fibrous protein composed of coiled-coil motifs, is a major structural component of ciliary rootlets and is essential for understanding ciliary functions. However, the precise mechanisms by which Rootletin influences ciliary dynamics and impacts neuronal function remain largely unknown, primarily due to the challenges in visualizing these structures. Here, we describe a label-free, rapid, and highly sensitive method to visualize Rootletin molecules in brain tissue. This platform integrates a second harmonic generation (SHG) microscope and background reduction by a one-step chemical pretreatment. Additionally, we employ coherent anti-Stokes Raman scattering imaging to simultaneously determine the cellular regions and intracellular locations of SHG signals. By applying this multimodal multiphoton imaging to mouse hippocampus, we found that neuronal ciliary rootlets were found to exhibit highly organized specific intracellular distributions. Moreover, the formation of ciliary rootlets precedes that of primary cilia. These findings highlight the utility of our label-free imaging platform in developmental and neuroscience research, providing a new tool to characterize ciliary dynamics and neuronal function.

biophysics↗