Photothermal cantilever deflection spectroscopy

Abstract

Real-time chemical sensing based on PCDS has many advantages. It does not use any chemical receptors or interfaces for molecular recognition. The cantilever used in this technique has no surface functional groups. The target molecules are physisorbed from vapor phase onto the surface with no chemical interaction with the substrate. This approach overcomes the reproducibility problems encountered with immobilized receptor-based approaches. Samples can be deposited on the cantilever by placing a drop of solution and drying it in the ambient temperature. Since signal generation is based on the resonance excitation of various molecular bonds in the target molecule, the method is extremely selective. In a complex mixture, the resultant signal is a linear combination of molecular vibrations from various constituents and can be discerned using simple pattern recognition techniques. The PCDS combines the extreme high-thermal sensitivity of a bi-material microcantilever beam with the selectivity of mid-IR molecular spectroscopy. Our earlier results have shown mass sensitivity of 10 pg on the cantilever under ambient condition (corresponding to a few monolayers of analyte).14 The magnitude of the IR absorption-induced cantilever bending is proportional to the amount of analyte on the cantilever. This can be further quantified by measuring the resonance frequency of the cantilever (mass loading). PCDS is a simple technique that can offer high chemical selectivity. The demonstrated sensitivity and selectivity of this approach offers new possibilities for receptor-free sensing of a wide range of materials beyond what is currently possible using conventional techniques. These devices have the obvious advantages of requiring only sub-nanogram samples, quick detection times, and the potential to be inexpensive. It is possible to increase the sensitivity of photothermal cantilever deflection spectroscopy by optimizing the bi-material cantilever parameters as well as increasing the power of the illuminating IR source