Acoustic Wave Catalyzed Urea Detection Utilizing a Pulsatile Microdroplet Sensor

Abstract

We observe variations in the electrical resistance across a conducting water microdroplet when it was placed on a glass substrate before being mechanically vibrated at natural frequency with the help of an acoustic source. The reduction in the resistance across the droplet was magnified owing to the formation of vortices in the matrix when the periodic oscillation of the surface was increased. The variation in the resistance could be tuned with the frequency of the sound source, which was found to be maximum when a 10 μL droplet was vibrated at ∼320 Hz. Interestingly, the variation in resistance across the oscillating droplet could follow and distinguish the musical notes in the octaves (“sur”) or rhythmic cycles (“taal”) originating from musical instruments such as flute, harmonium, whistle, and tabla. Further, when a suspension of urease-stabilized gold–cadmium–sulfide nanocomposite was suspended inside the droplet and mixed with an analyte containing urea solution, the change in the resistance during the operational time period was found to monotonically vary with the concentration of urea in the analyte. The enzymatic reaction between urea and urease was found to follow a faster first-order chemical kinetics than the commonly observed Michaelis–Menten pathway owing to the presence of the moving nanocomposites and mixing vortices under the optimal acoustic excitations. The specific lock-and-key enzymatic reaction helped in extending these experimental results to estimate the unknown levels of urea in human blood serum samples.

Printed Chipless Antenna as Flexible Temperature Sensor

“…These advances have allowed connecting different type of sensors to the cyberspace for applications such as environment monitoring, wearable systems for health monitoring, and security [8][9][10]. Several types of sensors used in these application include sweat [11], temperature [12], strain [13], pH [14], radiation [15], volatile organic compounds [16,17] and biomarkers for health [18,19] and environment etc. A variety of flexible substrates have been used for the development of these sensors.…”

Recent advancements in urea biosensors for biomedical applications

“…The acoustics caused mechanical noise enabling the enzymatic lock‐and‐key reaction among analyte urea and enzyme urease through amplified mixing. The latest conceptual prototype could become a low‐cost and viable solution for point‐of‐care detection [ 116 ]. A potentiometric nanocomposite urea biosensor has been developed.…”

Microdroplet based disposable sensor patch for detection of α-amylase in human blood serum

“…In this regard, a wide range of biosensors have been reported recently to evaluate the biomarkers in sweat, tears, urine etc. (Dang et al 2018;Kafi et al 2019;Manjakkal et al 2019;Middya et al 2019;Thakur et al 2019) to indicate the potential onset of diseases.…”