A Novel Photoacoustic Microsensor for Enhanced Quality Factor Detection of Low Concentration Analytes

This paper reports a novel microsensor for noninvasive photoacoustic biosensing in clinical diagnostic applications. The sensing platform utilizes the resonance mode of a vacuum-packaged Si microcantilever to detect and resolve the weak acoustic waves generated by the photoexcitation of the test analytes. The hermetic packaging not only overcomes the viscous degradation of acoustic signals but also yields ∼10-folds improvement in the limit of detectable pressure waves that is proportional to the square root of the quality factor. This approach allows the tuning of optical excitation frequencies close to the resonance mode of the microcantilever resulting in higher SNR compared to piezoelectric detection. Microsensor demonstrates the ability to resolve small variations of sample concentrations complementing the traditional analytical methods. The results show a high-resolution sensitivity of ∼5 ppm of the studied samples. This approach is the first attempt to exploit the benefits of resonance characteristics of a microcantilever with an enhanced quality factor for photoacoustic detection.