Combined colorimetric and gravimetric CMUT sensor for detection of phenylacetone

Abstract

The detection of phenylacetone is of interest as it is a common precursor for the synthesis of (meth)amphetamine. Resonant gravimetric sensors can be used to detect the mass and hereby the concentration of a gas while colorimetric arrays typically have an exceptional selectivity to the target analyte if the right colorimetric dyes are chosen. We present a sensor system consisting of a Capacitive Micromachined Ultrasonic Transducer (CMUT) and a colorimetric array for detection of phenylacetone. The CMUT is used as a resonant gravimetric gas sensor where the resonance frequency shift due to mass loading of the plate. A single Local Oxidation of Silicon (LOCOS) step was used to define the cavities which were sealed with a Si3N4 plate with a thickness of 100 nm, resulting in a resonance frequency of 38.8 MHz and a theoretical mass sensitivity of 28.3 zg Hz•µm 2. The CMUTs were functionalized with the same dyes used to fabricate colorimetric arrays. While both the CMUTs and the colorimetric arrays showed selectivity to phenylacetone, the best selectivity was achieved by the colorimetric array. Furthermore, the mass of the phenylacetone was found as a function of time. Thus, the combination of the colorimetric array and the CMUT results in a good selectivity and a quantitative value for the mass.

Methylated Poly(ethylene)imine Modified Capacitive Micromachined Ultrasonic Transducer for Measurements of CO2 and SO2 in Their Mixtures

“…For CMUT, the quality factor usually does not reach above 100, using the most popular fabrication methods, such as wafer bonding and sacrificial release [37,55,56]. However, when thin plates and very thin vacuum gaps are formed, it is possible to obtain quality factors over 100 [57,58] and other researchers have also shown an impressive quality factor of 400 [34].…”

Selective Ultrasonic Gravimetric Sensors Based on Capacitive Micromachined Ultrasound Transducer Structure—A Review

“…The viability of SUGS based on the CMUT structure was proven several times since previous decades. Very high resolution or limit of detection was demonstrated for DMMP [ 5 ], organic compounds [ 3 ], and CO 2 [ 9 , 10 ] detection. Additionally, the CMUT-based SUGS concept was proven to be suitable for biosensing [ 11 , 101 ].…”

“…Sensitivity can be increased by having a resonating micro membrane at a high frequency with very low mass. It was already shown by other researchers that a theoretical sensitivity of 0.45 Hz/ag can be achieved by a CMUT-based gravimetric sensor device [ 2 , 3 ]. The sensitivity can be optimized based on the selected resonance frequency by decreasing the mass of the resonating plate, which can easily be achieved by making them as thin as possible.…”

“…Application of ultrasonic transducers for sensing has become popular among multiple areas that include sensing of various physical, chemical, and biochemical phenomena. While several microelectromechanical system (MEMS) structures, like cantilevers, bridges, thin-film, or printed piezoelectric devices, can be applied for the ultrasonic sensing, the capacitive micromachined ultrasound transducers (CMUT) concept is highly advantageous due to the unprecedented sensitivity potential, good integration with electronics, hermetic active structure, high redundancy of the resonators, and CMOS (Complementary Metal-Oxide-Semiconductor) compatible fabrication process [ 1 , 2 , 3 ]. Gravimetric detection is a method that determines the quantity of the analyte (the molecule, species, or material of interest) by determining its mass.…”

“…Here, sensitivity describes the steepness of the main sensor function, usually characterized as a mass unit per the frequency unit. For this parameter, CMUT structure has little competition, since it was demonstrated by several groups to reach numbers down to 10 −18 g/Hz and below [ 2 , 3 , 4 , 5 , 6 , 7 , 8 ]. As for the other two parameters, they are more related to the properties of the functional material of the sensor [ 1 , 7 , 9 , 10 , 11 , 12 ], and the topic of the functional materials suitable for SUGS remains highly underexplored.…”