Robust, low-cost, and compact devices are the desired features of lab-on-a-chip platforms for electroanalytical applications. Paper-based wax printed devices have limitations such as large patterning features, lacking material toughness, and reliance on a heating step to permanently create features so that devices can work. Here, we introduce a new class of devices so-called “wax-on-plastic” by patterning wax on polyethylene terephthalate (PET) substrate to overcome the limitations of paper substrates. We present here wax-on-plastic electrochemical platforms that are tough, easy to fabricate, easy to modify with nanomaterials of superior electrochemical properties, and simple multiplexing. The first generation of these devices was fabricated by a combination of wax printing for patterning and hand painting of AgNPs for the electrode layer. The modification of the working electrodes of these devices with CNT performed as sensitive as commercial CNT-based screen-printed electrodes. Sandwich-based immunoassay was performed to detect carcinoembryonic antigen on magnetic beads and the electroactive end-product was amperometrically detected on the electrodes with a detection limit down to 0.46 ng/mL, i.e. 10x lower than the normal range. The second generation of the devices was fabricated by a combination of wax patterning and inkjet printing of AgNPs, which reduced the time of electrode layer patterning from 30 minutes to 5 seconds. The modification of working electrodes with inkjet printable MoS<sub>2</sub> ink allowed label-free detection of CGG trinucleotide repeat associated with Fragile X-associated ataxia in patient-derived cells at picomolar regime monitoring the electrocatalytic response of these sequences. The third generation of the devices shows high throughput fabrication of multiplexed chips with 372 electrodes patterned within the area of a smartphone. The bending and folding tests reveal that these devices are functional even kept folded for many days.

Wax-on-plastic electrochemical sensors: a new class of lab-on-chip devices

ACS Fall 2021

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