Moving towards in pouch diagnostics for ostomy patients: exploiting the versatility of laser induced graphene sensors

Abstract

The development of a 3D printed sensor for direct incorporation within stoma pouches is described. Laser induced graphene scribed on either side of polyimide film served as the basis of a 2 electrode configuration that could be integrated within a disposable pouch sensor for the periodic monitoring of ileostomy fluid pH. The graphene sensors were characterised using electron microscopy, Raman spectroscopy, DekTak profilometry with the electrochemical properties investigated using both cyclic and square wave voltammetry. Adsorbed riboflavin was employed as a biocompatible redox probe for the voltammetric measurement of pH. The variation in peak position with pH was found to be linear over pH 3-8 with a sub Nernstian response (43 mV/pH). The adsorbed probe was found to be reversible and exhibited minimal leaching through repeated scanning. The performance of the system was assessed in a heterogeneous bacterial fermentation mixture simulating ileostomy fluid with the pH recorded before and after 96 h incubation. The peak profile in the bacterial medium provided an unambiguous signal free from interference with the calculated pH before and after incubation (pH 5.3 to 3.66) in good agreement with that obtained with commercial pH probes.

Supplementary information: The online version contains supplementary material available at 10.1007/s10853-023-08881-x.

Figure 1

Design methodology for in pouch autonomous monitoring.

Figure 2

a Individual components of the working (WE) and reference (RE) electrodes. b Cross section highlighting the dual layer nature of the probe. c The positioning of the sensing head within the probe body and protective cap.

Figure 3

Electron micrographs detailing the LIG morphology arising from the x-y raster process (a, b) closer examination of the micro-nano porous carbon deposit (c, d).

Figure 4

Surface profiling across laser tracks formed from either a single or double pass. Subsequent removal of the LIG deposit via sonication allowed the etch depth to compared.

Figure 5

a Cyclic voltammogram detailing the response of a 2-pass LIG electrode to ferrocyanide (2 mM, pH 7, 50 mV/s) and b Raman spectrum of the LIG substrate after single and double pass ablation scans.

Figure 6

a Redox process associated with riboflavin. b Square voltammogram detailing the response of a riboflavin modified LIG electrode in Britton Robinson buffers of varying pH.

Figure 7

Variation of riboflavin oxidation peak (E_pa) with successive exposure to Britton Robinson buffer of varying pH.

Figure 8

a Square wave voltammograms highlighting the response of the 2-electrode LIG-riboflavin probe in a heterogeneous kefir suspension before and after the addition of the protective cap and b comparing the response after incubation for 96 h.