Paper-based graphene oxide biosensor coupled with smartphone for the quantification of glucose in oral fluid.

Rapid, disposable, point-of-care (POC) oral fluid testing has gained considerable attention in recent years as saliva contains biomarker and components of the serum proteome that offer important information on both oral and systemic disease. Microfluidic paper-based analytical devices (μPADs) coupled with smartphone reflectance sensing systems have long been considered to be an effective POC tool for the diagnostics of biomarkers in oral fluid. However, the existing portable systems are limited by the poor color distribution in the detection area as well as not being universally applicable. Therefore, using the properties of nanomaterials to our advantage, we present a simple, universally applicable approach that features graphene oxide (GO) coated μPADs coupled with smartphone-based colorimetric detection for the direct quantification of glucose. An integrated portable system is used to implement the approach. Owing to the enhanced reagents absorptivity, reactive efficiency and homogeneity of color distribution from the deposition of GO, the glucose assay performance was improved. Also, by using a self-developed app, the glucose concentrations in physiological range can be automatically quantified. Finally, the approach is universally applicable as the modification of μPADs with GO can be achieved without the use of any linker, binder or retention aid, which avoids possible enzyme cross contamination. The system was first calibrated by standard glucose buffer solutions, and the limit of detection as well as the linear dynamic range were found to be 0.02 mM and 0~1 mM, respectively, which are appropriate for analyzing glucose concentrations in a clinically relevant range. Finally, the system was used for quantifying glucose concentrations in artificial saliva and the results obtained using our portable system showed reasonable agreement with the actual use concentrations. Thus, the utility of the system in sensitively quantifying glucose concentrations in a portable, and repeatable manner is demonstrated.