Due to light dispersion and absorption, imaging deep into tissues is challenging. The wavelength windows for high-resolution deep mouse brain imaging are around 1300 nm and 1700 nm. However, due to the low detection efficiency of currently available detectors, one-photon fluorescence imaging in the wavelength region has proved extremely difficult.
Researchers have created one-photon confocal fluorescence imaging of deep mouse brains with an excitation wavelength and an emission wavelength within the 1310 nm – 1700 nm window to fully exploit this wavelength advantage. A custom-built superconducting nanowire single-photon detector (SNSPD) tuned for detection in the 1600 nm – 2000 nm range (with low detection noise and high detection efficiency) observed fluorescence emission at 1700 nm.
In vivo one-photon confocal fluorescence imaging was demonstrated at 1.7 mm below the surface of the mouse brain (through the entire cortical column and into the hippocampus region). They used a low-cost continuous-wave laser source and low excitation power using PEGylated quantum dots, and SNSPD positioned at the optimal imaging window for deep tissue penetration.