Non-contact molecular specific transient absorption microscopy

Monitoring dynamic activity of biochemical pathways is an essential, but challenging, step for diagnosing, treating, and understanding human pathologies. Transient absorption is a resonant two-photon optical imaging technique capable of probing multiple molecular-specific properties, such as ground state recovery time, absorption spectra, and transient absorption spectra, all with high resolution. Previously, photoacoustic based transient absorption imaging approaches have demonstrated the ability to probe ground state recovery time of biomolecules and provide spatial contrast on par with confocal microscopy. A fundamental challenge of these approaches relied on overlapping the focus of an ultrasound transducer with the optical focus for image detection, making the technique challenging to perform in vitro or in vivo. Here, we present non-contact methods for detecting transient absorption via the photoacoustic effect. These methods not only circumvent the need for ultrasound transducers but also enable integration with existing fluorescence imaging techniques.