Fully Inkjet-Printed Flexible Graphene-Prussian Blue Platform for Electrochemical Biosensing

Abstract

Prussian Blue (PB) is commonly incorporated into screen-printed enzymatic devices since it enables the determination of the enzymatically produced hydrogen peroxide at low potentials. Inkjet printing is gaining popularity in the development of electrochemical sensors as a substitute for screen printing. This work presents a fully inkjet-printed graphene-Prussian Blue platform, which can be paired with oxidase enzymes to prepare a biosensor of choice. The graphene electrode was inkjet-printed on a flexible polyimide substrate and then thermally and photonically treated with intense pulsed light, followed by inkjet printing of a PB nanoparticle suspension. The optimization of post-printing treatment and electrode deposition conditions was performed to yield a platform with minimal sheet resistance and peak potential differences. A thorough study of PB deposition was conducted: the fully inkjet-printed system was compared against sensors with PB deposited chemically or by drop casting the PB suspension on different kinds of carbon electrodes (glassy carbon, commercial screen-printed, and in-house inkjet-printed electrodes). For hydrogen peroxide detection, the fully inkjet-printed platform exhibits excellent sensitivity, a wider linear range, better linearity, and greater stability towards higher concentrations of peroxide than the other tested electrodes. Finally, lactate oxidase was immobilized in a chitosan matrix, and the prepared biosensor exhibited analytical performance comparable to other lactate sensors found in the literature in a wide, physiologically relevant linear range for measuring lactate concentration in sweat. The development of mediator-modified electrodes with a single fabrication technology, as demonstrated here, paves the way for the scalable production of low-cost, wearable, and flexible biosensors.

Keywords: Prussian Blue; enzymatic sensor; flexible biosensor; inkjet printing; intense pulsed light; lactate sensor; sweat lactate.

Figure 1

Schematic representation of the inkjet-printed electrode assembly and modification.

Figure 2

PBNP suspension characterization. (a) Photo of a freshly prepared PBNP suspension, (b) UV/Vis spectrum of the suspension, (c) stability of the suspension during 4 h, (d) size distribution obtained by DLS, (e) ζ-potential obtained by ELS, and (f) fully inkjet-printed graphene–PBNP platform.

Figure 3

IPL treatment optimization of inkjet-printed graphene electrodes. (a) Sheet resistance measurements via four point probe measurements (inset shows the significant drop of sheet resistance of the electrode after treatment compared to the unprocessed electrode); (b) peak separation in cyclic voltammograms (PW↔PB) at 10 mV/s recorded on an inkjet-printed electrode chemically modified after corresponding treatment.

Figure 4

Electrochemical characterization results for optimized deposition methods on inkjet-printed electrodes (top row: chemical deposition 20 min; bottom row: drop-cast PBNP, 10 μL). (a) Activation in 0.1 M KCl (scan rate 50 mV/s); (b) scan rate dependence recorded in 0.1 M KCl (10–100 mV/s); (c) pH stability of deposited films shown as cathodic peak current value extracted from cyclic voltammograms recorded in buffers (pH 5.4, 6.4 and 7.4).

Figure 5

SEM images of optimized PB-modified inkjet-printed electrodes: (a–c) chemically deposited PB ((a)—6k magnification, (b)—20k magnification, (c)—EDS mapping at lower magnification); (d–f) drop-cast PB nanoparticles ((d)—6k magnification, (e)—20k magnification, (f)—EDS mapping at lower magnification).

Figure 6

H₂O₂ detection with chronoamperometry ((1)—chronoamperograms and (2)—calibration curves) on electrodes modified by (a) 20 min chemical deposition, (b) drop casting 10 µL of PBNP suspension, (c) fully inkjet printing the PBNP suspension.

Figure 7

Lactate detection with chronoamperometry on fully assembled inkjet-printed sensor ((1)—chronoamperograms and (2)—calibration curves for electrodes modified by (a) 20 min chemical deposition, (b) drop casting 10 µL of PBNP suspension, (c) fully inkjet printing the PBNP suspension).