Hyperspectral near infrared imaging using a tunable spectral phasor

TL;DR

This paper introduces HyperNIR, a hyperspectral NIR imaging method using a tunable spectral phasor transformation with a liquid crystal retarder, enabling fast, label-free molecular and material identification in biomedical and environmental applications.

Contribution

The paper presents a novel hyperspectral NIR imaging technique using a spectral phasor approach with a tunable liquid crystal device, allowing rapid, label-free spectral discrimination with minimal images.

Findings

Achieves spectral resolution less than 5 nm between fluorophores.

Enables in vivo plant health monitoring and plastic polymer identification.

Reaches hyperspectral frame rates of 0.2 per second.

Abstract

Hyperspectral imaging captures both spectral and spatial information from a sample. The near infrared (NIR, > 800 nm) is advantageous for biomedical imaging as it falls into the tissue transparency window but also contains vibrational overtone and combination modes useful for molecular fingerprinting. Here, we demonstrate hyperspectral NIR imaging using a spectral phasor transformation (HyperNIR). This method employs a liquid crystal variable retarder (LCVR) for tunable, wavelength-dependent sine-, cosine and no filtering that transforms optical signals into phasor space. Spectral information is thus obtained with just three images. The LCVR can be adjusted to cover a spectral range from 900 nm to 1600 nm in windows tunable from 50 nm to 700 nm. This approach enables distinguishing NIR fluorophores with emission peaks less than 5 nm apart. Furthermore, we demonstrate label-free hyperspectral NIR reflectance imaging to identify plastic polymers and to monitor in vivo plant health. The approach uses the full camera resolution and reaches hyperspectral frame rates of 0.2 per second, limited only by the switching rate of the LCVR. HyperNIR facilitates straightforward hyperspectral imaging with standard NIR cameras for applications in biomedical imaging and environmental monitoring.