pH Meter-Assisted Biosensor Based on Glucose Oxidase-Conjugated Magnetic Metal–Organic Framework for On-Site Evaluation of Bacterial Contamination

There remains a critical need for the detection of bacterial contamination to ensure public health. In this work, we developed a pH meter-assisted biosensor based on glucose oxidase (GOx)-conjugated magnetic zeolitic imidazolate framework-8 (mZIF-8) for on-site evaluation of bacterial contamination. The mZIF-8/GOx conjugate was produced from the electrostatic interaction between GOx and mZIF-8 and was demonstrated to inhibit GOx activity without protein denaturation. However, the presence of bacteria can cause the release of GOx from the mZIF-8 surface through competitive binding with mZIF-8, resulting in the recovery of GOx activity, which converts glucose into gluconic acid and provides an amplified pH signal. This finding allows the mZIF-8/GOx conjugate to be a biosensor for on-site detection of bacterial contamination with a pH meter as a readout. Benefiting from the magnetic separation property of mZIF-8, greatly enhanced sensitivity and precision have been achieved with detection limits of 10 cfu/mL for Escherichia coli and 30 cfu/mL for Staphylococcus aureus. Meanwhile, the flexibility of this biosensor was validated by quantitative analysis of mixed bacteria including Gram-positive and Gram-negative bacteria with desired performances. The accurate bacterial determination in contaminated drinking water samples demonstrates the applicability of this biosensor for reliable home monitoring of water quality.