Sensitive non-enzymatic sensing of creatinine in urine using a novel paper-based electroanalytical device

Accurate analysis of urinary creatinine levels is of great clinical significance. Non-enzymatic creatinine sensing systems (NECSs) have gained growing development because of higher stability and lower cost compared to enzymatic sensing systems. At present, there is a demand for simple approaches to develop NECSs with high sensitivity. In this study, we designed and fabricated an ingenious paper-based electroanalytical device for sensitive non-enzymatic creatinine sensing in urine. The device consisted of a paper-based chip and an integrated three-electrode system. The quantification of creatinine was performed based on the complexation of creatinine and copper sulfate (Cu²⁺), which was pre-stored on the paper-based chip in advance. Under optimum conditions, the detection limit of creatinine was 0.26 μM with a linear range of 1-5000 μM. The relative standard deviations of the electroanalytical results (n = 3) were within 1.2%-5.4%. The proposed device showed excellent reproducibility and stability, and the current response remained 92.17% of the initial response after a 30-day storage. Moreover, the device also exhibited high anti-interference ability to a variety of chemical components in urine. This study presents a simple and robust approach to engineering NECSs with high sensitivity. The preparation of the whole system is based on accessible and reliable commercial technologies and materials, which minimizes manual operation and ensures good reproducibility. The sensitivity of our method is two orders of magnitude lower than those of the previously reported NECSs based on the solution-modification strategy. It has been applied to the analysis of human urinary creatinine with satisfactory recoveries and without significant differences compared with commercial creatinine assay kits.