# Off-resonant transient absorption microscopy

> **NIH NIH R21** · COLORADO STATE UNIVERSITY · 2020 · $221,234

## Abstract

Summary/Abstract
Transient absorption microscopy has enormous potential for providing label-free imaging
contrast from endogenous molecules. However, the technique is seriously limited by its
requirement for UV/visible-wavelength interactions. At these wavelengths, optical absorption
and scattering are high, limiting penetration depth, causing excess sample heating, which in turn
limits the amount of power that can be applied and signal-to-noise levels that can be recorded.
We propose a new approach to transient absorption that mitigates the disadvantages inherent
to resonant interactions, while maintaining the multiphoton advantages that motivated its original
development. The new approach will open a pathway for transient absorption imaging deep
inside of tissues, while improving image quality and expanding the technique to its full range of
endogenous molecular targets for label-free in vivo imaging. Aim 1 will move the probe to near-
infrared wavelengths, using transient phase detection with a stable inline interferometry
technique. Aim 2 will move the pump to the near-infrared region using two-photon absorption.
Together, these approaches will eliminate the need for UV/visible wavelengths (resonant
absorption), and thereby mitigate the technical hurdles limiting more widespread use of transient
absorption microscopy. This new technique will have broad applicability to advance biomedical
research, with potential direct clinical applications, for example basic tumor biology and study of
microenvironment and chemoresistance, diagnosis and quantitative follow-up of mitochondrial
diseases, and staging and surgical planning for melanoma. The off-resonant transient
absorption microscopy to be developed in this R21 will open new vistas in molecular imaging
targets with high spatial resolution deep inside of tissues.

## Key facts

- **NIH application ID:** 9877931
- **Project number:** 1R21GM135772-01
- **Recipient organization:** COLORADO STATE UNIVERSITY
- **Principal Investigator:** Randy A. Bartels
- **Activity code:** R21 (R01, R21, SBIR, etc.)
- **Funding institute:** NIH
- **Fiscal year:** 2020
- **Award amount:** $221,234
- **Award type:** 1
- **Project period:** 2020-01-01 → 2021-12-31

## Primary source

NIH RePORTER: https://reporter.nih.gov/project-details/9877931

## Citation

> US National Institutes of Health, RePORTER application 9877931, Off-resonant transient absorption microscopy (1R21GM135772-01). Retrieved via AI Analytics 2026-05-23 from https://api.ai-analytics.org/grant/nih/9877931. Licensed CC0.

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