Development of multimodal sensing devices for receptor-free molecular detection and quantification

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Detection, differentiation, and quantification of trace amounts of chemical and biological molecules with a portable device are of great interest in many applications such as energy, environment, law-enforcement, and health. Chemical and biological sensors based on micro/nanoelectromechanical systems (MEMS/NEMS) offer many advantages such as high sensitivity, miniature size, multiple detection, and low-power consumption. However, obtaining chemical selectivity in MEMS/NEMS sensors using chemoselective interfaces (for example, self-assembled monolayer, polymer coating, receptors, etc.) has been a longstanding challenge. Despite their many advantages, MEMS/NEMS devices relying on chemoselective interfaces do not have sufficient chemical selectivity. Chemical selectivity based on weak molecular interactions is partially specific even when an array format like an electronic nose is used. On the other hand, biological sensing based on receptors such as aptamer, antibodies, and peptides is thought to be very selective, but suffers from non-specific adsorption of non-target background molecules, limited shelf-life, and lack of robust and reproducible receptor immobilization methods. Therefore, highly sensitive and selective detection, differentiation, and quantification of chemical and biological molecules using real-time, miniature sensor platforms still remains as a crucial challenge. Currently available technologies, such as ion mobility spectrometry, gas chromatography-mass spectrometry, and labeled fluorescence spectroscopy are usually bulky, time-consuming, and expensive. Therefore, the development of new miniature multimodal sensing platforms which are not relying on chemoselective interfaces but being selective and quantitative is very attractive.**Incorporating photothermal/photoacoustic spectroscopic techniques with MEMS/NEMS can provide the chemical selectivity without sacrificing the sensitivity of miniaturized sensing devices. For example, photothermal cantilever deflection spectroscopy, which combines the high thermal sensitivity of a bimetallic microcantilever with the high selectivity of mid infrared (IR) spectroscopy, is capable of obtaining molecular signatures of extremely small quantities of adsorbed molecules (tens of picogram level). Conventional IR spectroscopy, which relies on Beer-Lambert's law, is based on detecting small intensity changes in transmitted light through a sample using a cryogenically cooled IR detector. Increasing the incident IR power increases the inherent background signal without enhancing the signal-to-noise ratio (SNR). In contrast, in photothermal/photoacoustic IR spectroscopy with MEMS/NEMS, IR absorption induces changes in the sample temperature and these minute temperature changes are transduced by MEMS/NEMS, which results in an enhanced SNR with increased incident IR power. By employing a broadly tunable, high power quantum cascade laser, the proof-of-concept experiments were already performed and reported by the applicant.**Here the development of new multimodal sensing devices by integrating opto-mechanical spectroscopy components into micro/nano-devices which can be fabricated using micro/nanofabrication techniques is proposed. These new miniature sensors will work as a highly sensitive resonator as well as a thermometer which can provide at least two orthogonal signals such as mass and spectral information of adsorbed molecules. The combination of information from these devices will provide the extremely high sensitivity and selectivity needed for chemical and biological agent detection, differentiation, and quantification. These multimodal sensing devices will find immediate applications in energy, environment, law-enforcement, and health for the welfare of all Canadians.