This work presents a proof of concept point-of-care urea biosensor that incorporates a facile but robust detection technique and by virtue of its configuration, is also disposable. To substantiate, variations in the electrical resistance across a conducting water microdroplet placed on a glass substrate was observed when it was subjected to sinusoidal acoustic waves at its natural frequency. It was observed that for a 10 µL droplet resting on a glass substrate, acoustic waves of ~ 320 Hz frequency caused the maximum deformation and subsequently the maximum change in electrical resistance of the droplet. For the biosensing application, the conducting water microdroplet was loaded with a suspension of urease-linked gold/cadmium sulfide nanocomposite. Upon adding urea solution in the droplet under the influence of acoustics waves, the changing electrical resistance could be effectively correlated with the changing urea concentration. The nanocomposite enhanced enzymatic reaction followed faster first-order reaction kinetics than Michaelis-Menten pathway because of: firstly, nanocomposites presence acted as a scaffold for the enzyme moieties providing them with stability, enhanced interfacial area and secondly, oscillatory behavior of the microdroplet in a confined system resulted in formation of vortices that improved the mixing characteristics. Studies were also performed utilizing various concentrations of urea [1-150 mM] with a fixed enzyme concentration, to prepare a calibration chart which was eventually utilized for determining unknown urea concentration in human serum samples. Thus the potential of this setup as a urea biosensor was demonstrated. Additionally, this setup’s utility could also be extended to another diverse application such as sound sensing without much alteration to the system’s geometry. Upon exposing the droplet to different sounds issuing from three distinct Indian classical instruments, variations in the electrical resistance of the droplet could interestingly, follow the different musical notes and the rhythmic cycles. Thus the microdroplet setup could also be employed as a sound sensor. 

Oscillatory microdroplet constituted urea biosensor stimulated by acoustic waves

Macromolecular Chemistry: The Second Century

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ACS Spring 2020 National Meeting & Expo

The official archive and repository for all ACS Meetings & Expositions abstracts and select posters or presentations.