Vancomycin is one of the most important anti-bacterial drugs for the treatment of MRSA infection. Continuous monitoring is commonly recommended as it has a low therapeutic window, which is often limited by the equipment cost, and the technical skills required for modern TDM techniques such as HP-LCs and immunoassays. As a result, a cost-effective and quick detection solution for Vancomycin TDM is critical. We have already reported a successful vancomycin sensor on a ceramic base, a paper base, and a PET (polyethylene terephthalate) base, in our previous works ^1,2. However, the long-term stability of the sensor for the clinical trial is very important. Therefore, this study focused on the improvement of the stability of the sensor.

The PET chip is composed of a PET base on which the silver wiring was printed using an inkjet printer. It contains two holes for electrodes with a 2.0 mm diameter for the counter electrode and a 1.0 mm diameter for the working electrode. The chip also comprises a circular reservoir of diameter 8 mm. VCM imprinted poly(methylene bisacrylamide-co-methacrylic acid-co-Allylaminocarboxypropyonic-3-ferrocene) was grafted on graphite particle surface by a procedure similar to our previous work. This grafted graphite was mixed with a) silicon oil (MIP_si), and b) paraffin oil (MIP_pff) to make a paste to use as the sensing material. The viscosity of both the oils was the same. We performed the chronoamperometric analysis with a VCM sample solution (0-60 µgmL^-1, in phosphate buffer) filled in the sample reservoir.

The chronoamperometric analysis time was 15 seconds for each sample. Current obtained at the 10^th second was recorded to obtain the calibration curve. The change in current at 10s demonstrated strong linearity with the VCM concentration in both MIP_si and MIP_pff, indicating good linearity with the change in current at 10s. Furthermore, this result was obtained using a "single-use" chip, which implies that each concentration was measured using a separate chip. MIP_si and MIP_pff were both sensitive to vancomycin. However, when the sensor was packed and kept for 3 days, the MIP_si sensor lost its sensitivity completely. Sensor with the working electrode made of MIP_pff, however, retained their sensitivity. MIP_pff was further packed and kept for 10 days to have a deeper insight into the effect of binder oil on the long-term stability of the sensor and the sensor was still found to be sensitive. From the results of this study, it can be concluded that a stable sensor that can sensitively detect vancomycin can be made using paraffin oil as the binder oil.

References

1. Aaryashree, A., Takeda, Y., Yoshimi, Y., Hatano, A. & Kida, M. A Disposable Vancomycin Sensor Using Molecularly Imprinted Carbon Paste on a Ceramic Chip. in ECS Meeting Abstracts vols MA2020-02 3332–3332 (2020).
2. Aaryashree et al. A “Single-Use” Ceramic-Based Electrochemical Sensor Chip Using Molecularly Imprinted Carbon Paste Electrode. Sensors 20, 5847 (2020).