Highly sensitive supra-molecular thin films for gravimetric detection of methane

This report discusses two deposition methods for the preparation and deposition of thin films of Cryptophane A for gravimetric detection of methane. The first method relies on electrospinning of Cryptophane A with carrier polymers. The second technique is based on spin coating of a mixture of Cryptophane A, tetrahydrofuran, and SU8-3000 followed by curing. The required Cryptophane A molecules were synthesized using an improved 2-step trimerization method. Both methods offer good control over the uniformity and thickness of the deposited layers. Moreover, both techniques improved the performance of the gravimetric sensor due to the higher possible quality factors of the resonant sensors. The responses of methane sensors based on both methods were characterized using various concentrations of methane. The prototype sensors had an estimated detection limit of about 3 ppm with a sensitivity of 80 mHz/ppm. Both parameters show improvement over the previously reported works. Our research demonstrates that electrospinning of Cryptophane A films generally results in a higher quality factor for the gravimetric sensors, and thus, improved sensor resolution.