Abstract
Graphene oxide modified screen-printed electrodes have been tested as amperometric sensors for morphine determination. The results demonstrate that the arising of electrocatalytic processes ascribable to the graphene coating, combined with the use of a suitable cleaning procedure, allow the sensor to achieve higher sensitivity (2.61 nA ppb−1) and lower limit of detection (2.5 ppb) with respect to those reported in the literature for similar devices.Due to very low detection limit found, the device is suitable to detect the presence of morphine in urine samples after a very simple and rapid pre-treatment of the matrix, allowing the removal of interfering species affecting the voltammetric responses. Tests performed in synthetic urine samples demonstrate that the presence of the electrocatalytic coating is mandatory in resolving the peak due to morphine oxidation in respect to uric acid. The sensor proposed is, thus, suitable to detect this drug even at concentration values below the cut-off levels defined by European and American regulations. These results allow us to propose the sensor for screening tests in portable devices, to be applied in systematic controls of drug abuses, e.g. in drivers and in men at work.
Highlights
Morphine is a highly effective drug for the treatment of severe pains, because it acts directly on the central nervous system, where it mimics the effects of the endorphins, i.e. endogenous neuropeptides possessing powerful analgesic and exciting activity
cyclic voltammetric (CV) responses evidence that ΔE is similar to that measured at bare screen-printed electrode (SPE), indicating a lower resistance of the exfoliated graphene oxide (EGO) film with respect to coatings obtained by deposition of graphene oxide produced by Hummer method [38], constituting the synthetic approach more frequently adopted
The evaluation of the electrocatalytic behaviour of EGO coatings with respect to morphine oxidation was performed by comparing CV traces collected at bare and at modified SPEs, in phosphate buffer solution (PBS) only containing the analyte
Summary
Morphine is a highly effective drug for the treatment of severe pains, because it acts directly on the central nervous system, where it mimics the effects of the endorphins, i.e. endogenous neuropeptides possessing powerful analgesic and exciting activity. Morphine itself is considered an illicit drug, exhibiting potentially serious side effects, such as slow respiratory rate and low blood pressure, and constitutes an indicator of abuse of other opioids, being one of their metabolites [4] Due to all these effects, this analyte requires to be strictly monitored in many environmental and biological samples. It should lead to an as low as possible number of false negatives, i.e. of responses that are erroneously estimated to be within the noise confidence interval, whereas a limited number of false positives does not constitute a serious drawback Several progresses along this direction have been recently made by the development of amperometric sensors, which base the detection on the occurrence of electrochemical oxidation of morphine. Screening tests of morphine in the real matrix were found possible after the development of a very rapid and automatable sample pre-treatment
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