An inexpensive disposable electrochemical drug sensor for the detection of drugs (vancomycin, meropenem, theophylline, and phenobarbital) is described. Molecularly imprinted polymer (MIP) templated with the target drugs was immobilized on the surface of graphite particles using a simple radical polymerization method and packed into the working electrode of a three-electrode ceramic-based chip sensor. Differential pulse voltammetry (DPV) was used to determine the relationship between the response current and the concentration of the targeted drug while using one sensor chip for one single operation. The time required for each DPV measurement was less than 2 min. Concentrations corresponding to the therapeutic range of these drugs in plasma were taken into account while performing DPV. In all the cases, the single-used MIP sensor showed higher sensitivity and linearity than non-imprinted polymer. The selectivity test in drugs with a structure similar to that of the target drugs was performed, and it was found that MIP-based sensors were more selective than the untreated ones. Additionally, the test in whole blood showed that the presence of interfering species had an insignificant effect on the diagnostic responses of the sensor. These results demonstrate that the disposable MIP-sensor is promising for quick and straightforward therapeutic drug monitoring to prevent the toxic side effects and the insufficient therapeutic effect due to the overdose and underdose, respectively.

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Introduction Molecularly imprinted polymers (MIPs) are recognition elements with specific cavities designed for a particular target molecule. Recently, MIPs have been used in various applications explicitly requiring molecular recognition. In MIPs, the crosslinking monomers and functional monomers, having an affinity with a target molecule, are copolymerized in the presence of the target or the template molecule. Upon selective removal of the template molecule, imprinted cavities are formed. MIPs provide a wide range of benefits, including mechanical reliability, cost-effectiveness, and rapid mass production, and have recently been used for various applications, especially in biosensing areas [1]–[3]. Theophylline (THO) is a drug commonly used for the therapy of respiratory diseases. However, owing to its highly toxic nature, an overdose can induce paralysis, seizures, and even death.[4] Additionally, the therapeutic window of THO is relatively small (5-15 mgmL-1) [4],[5], and therefore, the therapeutic drug monitoring (TDM) of theophylline is highly significant [5]. In this study, molecularly imprinted polymers grafted carbon pastes were prepared for THO sensing. The commonly used functional monomer, methacrylic acid, crosslinking monomers, N, N’-methylenebisacrylamide (MBAA), and ethylene glycol dimethacrylate (EDMA) were used, and the MIPs thus formed were evaluated using differential pulse voltammetry on a paper chip. Methods Fig. 1 shows the scheme of the paper chip along with the sensing response of theophylline MIP. The paper chip composed of a photo-paper base with electrodes printed using conductive ink through an inkjet printer. The holes for electrodes (working electrode, a reference electrode, and counter electrode) and reservoir are cut on laminating sheets using a laser cutter. The three parts are then attached using the laminator. The reference electrode is packed with Ag/AgCl ink and dried overnight at 60 ℃. The counter electrode with the printed conductive ink is used as it is. The MIP-grafted carbon paste is packed in the working electrode with the help of a glass tube. The theophylline imprinted poly(methylene bisacrylamide-co-ethylene dimethacrylate-co-methacrylic acid) was grafted on the graphite particle surface by a procedure similar to our previous work [3], [6]. This grafted graphite was mixed with ferrocene containing silicone oil to make a paste used as the sensing material. We performed the differential pulse voltammetry with theophylline sample solution (in saline buffer with pH 7.4, 0-40 mgmL-1 and whole bovine blood) filled in the sample-reservoir. Results and Conclusions The execution time of each voltammetry was 2 min only. The plot in Fig. 1 shows the influence of the theophylline concentration on the redox current at 0.8 V at the MIP-carbon paste electrode in both buffer saline and whole bovine blood. It is quite evident from the figure that MIP is sensitive towards theophylline in both buffer and whole blood. It indicates that MIP activates the electrocatalytic behavior of the carbon-paste electrode. The dynamic range at the MIP electrode versus the concentration of theophylline is seen in the range of 0-40 mgmL-1, which covers the therapeutically effective theophylline concentration level in plasma varying from 5 to 15 mgmL-1. The DPV measurements at each concentration has been done using a new chip every time, i.e. ‘single-use’ of the chip. Additionally, no reagents have been added during the analysis, thus making the procedure of drug level measurement simple. From the results of this study, it can be concluded that the proposed method is useful for quick and straightforward real-time TDM to prevent the toxic side effects of an overdose. References [1] T. Sakata, et al. RSC Adv., 10(29),16999–17013, 2020; doi:10.1039/d0ra02793f. [2] Y. Yoshimi, et al. Sensors, 19(10), 2415, 2019; doi:10.3390/s19102415. [3] Y. Yoshimi, et al. Sensors Actuators, B Chem., 259, 455–462, 2018; doi:10.1016/j.snb.2017.12.084. [4] R. Vassallo, et al. Mayo Clin. Proc., 73(4), 346–354, 1998; doi:10.1016/s0025-6196(11)63701-4. [5] A. Peng, Int. J. Electrochem. Sci., 12(1), 330–346, 2017; doi:10.20964/2017.01.03. [6] Aaryashree et al., Sensors, 20(20), 5847, 2020; doi:10.3390/s20205847 Figure 1

Introduction Vancomycin (VCM) is the first-choice drug for the therapy of MRSA infection, which is the most typical nosocomial infection. However, VCM resistant bacteria is a severe worldwide problem [1]. Therapeutic drug monitoring (TDM) of VCM in the blood is useful to prevent the creation of resistant bacteria. Nevertheless, conventional TDM using immunoassay requires economical and labor burdens to hospitals [2]. Thus, an inexpensive disposable sensor that can determine the VCM concentration in blood with simple operation as that of blood sugar-sensor is required. In this study, we developed a VCM sensor using a carbon paste electrode grafted with a molecularly imprinted polymer (MIP) and a ceramic platform. MIPs are a molecular recognition element prepared by simple radical copolymerization in the presence of the target as a template. We have discovered that redox current at a MIP-grafted carbon paste electrode is sensitive to the target [3]. Method Figure 1(a) shows the scheme of the ceramic chip composed of aluminum oxide ceramic body and platinum wiring. It contains three holes for electrodes with 2.0 mm diameter and 0.4 mm depth, connected with platinum wiring at the bottom. The chip also comprises a square sample-reservoir of side 10 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 [3], This grafted graphite was mixed with silicone oil to make a paste to use as the sensing material. A non-treated polymer was also synthesized in a similar way as that of VCM MIP, but without the template. Two of the holes of 2.0 mm diameter were each packed with grafted graphite and Ag/AgCl paste to act as the working electrode a reference electrode, respectively. The Pt wire of the third hole was used as the counter electrode. We performed differential pulse voltammetry with a VCM sample solution (0-60 mgmL-1, both in phosphate buffer and in bovine blood) filled in the sample-reservoir. Results and Conclusions The execution time of each voltammetry was 10 min only. Figure 1(b) shows the influence of the VCM concentration on the redox current at 0.8 V at both non-treated and the MIP-carbon paste electrode. It is quite evident from the figure that only MIP responds to VCM. The dynamic range at the MIP electrode versus the concentration of VCM is seen in the range of 0-60 mgmL-1, which corresponds covers the therapeutically effective vancomycin concentration level in plasma varying from 20 to 40 mgL-1 [4], [5]. Additionally, the R2 value of 0.9963 indicates a linear behavior of the sensor with change in drug concentration. From these results, it can be concluded that the proposed method is useful for quick and straightforward TDM to prevent both of the toxic side effects by overdose and the creation of antibacterials by underdose. References [1] Z.-K. Ye, et. al. PLoS One, vol. 8, no. 10, p. e77169, Oct. 2013,doi:10.1371/journal.pone.0077169. [2] K. Matsumoto, et. al. J. Infect. Chemother., vol. 19, no. 3, pp. 365–380, 2013,doi:10.1007/s10156-013-0599-4. [3] Y. Yoshimi, et. al. Sensors Actuators B Chem., vol. 259, pp. 455–462, Apr. 2018,doi:10.1016/j.snb.2017.12.084. [4] “UCSFMC Adult Vancomycin Dosing and Monitoring Recommendations.” https://idmp.ucsf.edu, 2018. [5] “Vancomycin in adult patients,” vol. 2018, May, 2017. Acknowledgment The research is partially supported by Grant in Aid of JST A-STEP. Figure 1