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Published September 2013 | Published
Journal Article Open

Noise-equivalent sensitivity of photoacoustics


The fundamental limitations of photoacoustic microscopy for detecting optically absorbing molecules are investigated both theoretically and experimentally. We experimentally demonstrate noise-equivalent detection sensitivities of 160,000 methylene blue molecules (270 zeptomol or 2.7×10^(−19) mol) and 86,000 oxygenated hemoglobin molecules (140 zeptomol) using narrowband continuous-wave photoacoustics. The ultimate sensitivity of photoacoustics is fundamentally limited by thermal noise, which can present in the acoustic detection system as well as in the medium itself. Under the optimized conditions described herein and using commercially available detectors, photoacoustic microscopy can detect as few as 100s of oxygenated hemoglobin molecules. Realizable improvements to the detector may enable single molecule detection of select molecules.

Additional Information

© 2013 SPIE. Paper 130345PR received May 13, 2013; revised manuscript received Aug. 4, 2013; accepted for publication Aug. 7, 2013; published online Sep. 11, 2013. This work was sponsored in part by the National Institutes of Health Grant Nos. DP1 EB016986 (NIH Director's Pioneer Award), R01 EB008085, U54 CA136398, R01 CA157277, and R01 CA159959. Lihong V. Wang has a financial interest in Microphotoacoustics, Inc. and Endra, Inc., which, however, did not support this work. Konstantin Maslov has a financial interest in Microphotoacoustics, Inc., which did not support this work.

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