Convolution of Analyte-Electrode Interactions over Distinct Time-Scales Leading to Taste Discrimination in Single Response Electroplated Metal Microwires-Based Microfluidic Electronic Tongue
Authors: Yadav Sarika , Sahu Rajendra Kumar , Pala Raj Ganesh 
Published: August 2024

A microfluidic electronic tongue (MET) is demonstrated via analyzing a single equivalent admittance spectrum derived from stainless-steel microwires electroplated with copper, nickel, iron, and zinc, all interconnected in parallel. These microwires were integrated into a microfluidic chip composed of polydimethylsiloxane (PDMS). A single admittance response for taste analytes, passing through micro-channels, was measured by short-circuiting the ends of multi-wire MET chip. The resulting admittance response from the MET was processed via principal component analysis (PCA) for visualization of clustering according to the taste groups. The performance of MET was assessed in terms of cluster analysis and Silhouette coefficient (SC).
This analytical method effectively clusters four primary taste samples based on their distinct flavor profiles, showcasing notable differentiation with a Silhouette coefficient surpassing 0.71. The elucidation provided by the biplot reveals that electronic and ionic interaction at analyte-electrode interactions over distinct time scales contribute synergistically towards discrimination of taste in dimensionally reduced 2-D PCA space. Real admittance responses at lower and higher frequency range contribute majorly in the composition of first and second principal components respectively. The equivalent electric circuit (EEC) was fitted to the developed MET to gain better understanding of response mechanism. A capacitor (C) in parallel to a series combination of resistor (R) and inductor (L), is (C[RL]) kind of EEC fitted to the admittance spectra. Interestingly, when relying on fitted equivalent electric circuit data, the taste discriminability of the MET is notably diminished as not all EEC elements are able to capture signature response specific to each taste. This observation critically evaluates the strategy of suitable data selection towards accurate and efficient taste discrimination as the admittance response over complete frequency range are pivotal contributors to the MET's impressive taste discrimination capabilities.
A pivotal aspect of the MET's functionality lies in deploying a single admittance response, a convolution of the responses of multiwire configurations integrated into the MET. This approach ensures global selectivity by utilizing copper, nickel, iron, and zinc electrodeposited stainless-steel microwires. These functionalization-free sensing units exhibit the ability to discriminate sweet, sour, bitter, and salty taste groups with remarkable clarity, boasting a Silhouette coefficient value of 0.77.
The MET's adaptability is further underscored by its electroplating modification, which is both expandable and enables clean room-free fabrication methods. This capability paves the way for the widespread manufacturing of MET chips featuring readily interchangeable and reusable calibration-free electrodes.
Looking ahead, the MET holds promise for future applications in quality control, particularly in the assessment of real food and beverage samples such as milk and soft drinks. The efficiency demonstrated in discriminating between tastes suggests that the MET could offer a cost-efficient and simplified solution for taste and quality assessments across diverse commercial applications. This potential extends to scenarios where clean room facilities are not readily available.
In summary, the MET's unique approach, utilizing a single equivalent admittance spectrum from electroplated metal wires in a microfluidic context, showcases robust taste discrimination capabilities. Integrating PDMS microfluidic chips and employing principal component analysis add layers of sophistication to the methodology. The MET's global selectivity, functionalization-free sensing units, and adaptability in manufacturing advocate its potential for revolutionizing taste and quality assessment in various industries, providing a glimpse into a future where simplicity and cost-efficiency are paramount considerations in analytical methodologies.