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- Electrochemical sensing of the thyroid hormone thyronamine (T0AM) via molecular imprinted polymers (MIPs)Publication . Pacheco, João; Rebelo, Patrícia; Cagide, Fernando; Gonçalves, Luís Moreira; Borges, Fernanda; Rodrigues, José António; Delerue-Matos, CristinaRecent studies have shown that besides the well-known T3 (triiodothyronine) and T4 (thyroxine) there might be other important thyroid hormones, in particular T0AM (thyronamine) and T1AM (3-iodothyronamine). The absence of a large number of studies showing their precise importance might be explained by the limited number of analytical methodologies available. This work aims to show an electroanalytical alternative making use of electropolymerized molecularly imprinted polymer (MIPs). The MIPs' polymerization is performed on the surface of screen-printed carbon electrodes (SPCEs), using 4-aminobenzoic acid (4-ABA) as the building and functional monomer and the analyte T0AM as the template. The step-by-step construction of the SPCE-MIP sensor was studied by cyclic voltammetry (CV) and by electrochemical impedance spectroscopy (EIS). After optimization, by means of square-wave voltammetry, the SPCE-MIP showed suitable selectivity (in comparison with other thyroid hormones and catechol amines), repeatability (intra-day of 3.9%), a linear range up to 10 μmol L-1 (0.23 × 103 μg dL-1) with an r2 of 0.998 and a limit of detection (LOD) and quantification (LOQ) of 0.081 and 0.27 μmol L-1 (1.9 and 6.2 μg dL-1), respectively.
- Breast cancer biomarker (HER2-ECD) detection using a molecularly imprinted electrochemical sensorPublication . Pacheco, João; Rebelo, Patrícia; Freitas, Maria; Nouws, Henri; Delerue-Matos, CristinaThe extracellular domain of the human epidermal growth factor receptor 2 (HER2-ECD) is a protein breast cancer biomarker. Its quantification in peripheral blood could provide an important contribution to diagnostics and patient follow-up. In this work an electrochemical molecularly imprinted polymer (MIP) sensor for the quantification of HER2-ECD was developed. The MIP was electropolymerized by cyclic voltammetry using a solution containing phenol and HER2-ECD on a screen-printed gold electrode (AuSPE). The sensor was characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The analysis of HER2-ECD was performed by differential pulse voltammetry using ([Fe(CN)6]3−/4−as redox probe. The linear range was established in the concentration interval from 10 to 70 ng/mL HER2-ECD, with a limit of detection of 1.6 ng/L and a limit of quantification of 5.2 ng/mL. Through the analysis of other protein biomarkers, the MIP sensor was found to be selective. Furthermore, these proteins did not interfere in the analysis of the selected biomarker. The developed sensor was used for the analysis of spiked human serum samples, providing adequate recovery values and precise results. The outcomes of this study indicate that the developed MIP sensor could be useful in the non-invasive analysis of HER2-ECD in breast cancer patients.
- A simple electrochemical detection of atorvastatin based on disposable screen-printed carbon electrodes modified by molecularly imprinted polymer: Experiment and simulationPublication . Rebelo, Patrícia; Pacheco, João; Voroshylova, Iuliia; Melo, André; Cordeiro, M. Natália D.S.; Delerue-Matos, CristinaAtorvastatin (ATV) is a statin member consumed in high quantities worldwide. In response to that, the occurrence of ATV in environmental waters has become a reality, highlighting the need of rapid and sensitive analytical devices for its monitoring. In this work, the first electrochemical molecularly imprinted polymer (MIP) sensor for the detection of ATV in water samples is presented. Computational studies were conducted based on quantum mechanical (QM) calculations and molecular dynamics (MD) simulations for rational selection of a suitable functional monomer and to study in detail the template-monomer interaction, respectively. The sensor was prepared by electropolymerisation of the selected 4-aminobenzoic acid (ABA) monomer with ATV, acting as template, on screen printed carbon electrode (SPCE). Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques were applied to characterise the modified electrode surfaces. The quantitative measurements were carried out with differential pulse voltammetry (DPV) in 0.1 M phosphate buffer (pH = 7). After investigation and optimisation of important experimental parameters, a linear working range down to 0.05 μmol L−1 was determined with a correlation coefficient of 0.9996 and a limit of detection (LOD) as low as 0.049 μmol L−1 (S/N = 3). High sensitivity and selectivity of the prepared sensor were demonstrated with the ability to recognise ATV molecules over its closer structural analogues. Moreover, the sensor was quickly and successfully applied in spiked water samples, proving its potential for future on-site monitoring of ATV in environmental waters.
- Electropolymerized, Molecularly Imprinted Polymer on a Screen-Printed Electrode—A Simple, Fast, and Disposable Voltammetric Sensor for TrazodonePublication . Seguro, Isabel; Rebelo, Patrícia; Pacheco, João; Delerue-Matos, CristinaIn recent years, analytical chemistry has been facing new challenges, particularly in developing low-cost, green, and easy-to-reproduce methods. In this work, a simple, reproducible, and low-cost electrochemical (voltammetric) molecularly imprinted polymer (MIP) sensor was designed specifically for the detection of trazodone (TZD). Trazodone (TZD) is an antidepressant drug consumed worldwide since the 1970s. By combining electropolymerization (surface imprinting) with screen-printed electrodes (SPCEs), the sensor is easy to prepare, is environmentally friendly (uses small amounts of reagents), and can be used for in situ analysis through integration with small, portable devices. The MIP was obtained using cyclic voltammetry (CV), using 4-aminobenzoic acid (4-ABA) as the functional monomer in the presence of TZF molecules in 0.1 M HCl. Non-imprinted control was also constructed in the absence of TZD. Both polymers were characterized using CV, and TZD detection was performed with DPV using the oxidation of TZD. The polymerization conditions were studied and optimized. Comparing the TZD signal for MIP/SPCE and NIP/SPCE, an imprinting factor of 71 was estimated, indicating successful imprinting of the TZD molecules within the polymeric matrix. The analytical response was linear in the range of 5–80 µM, and an LOD of 1.6 µM was estimated. Selectivity was evaluated by testing the sensor for molecules with a similar structure to TZD, and the ability of MIP/SPCE to selectively bind to TZD was proven. The sensor was applied to spiked tap water samples and human serum with good recoveries and allowed for a fast analysis (around 30 min).
- Molecularly imprinted electrochemical sensor prepared on a screen printed carbon electrode for naloxone detectionPublication . Lopes, Frederico; Pacheco, João; Rebelo, Patrícia; Delerue-Matos, CristinaNaloxone (NLX) is a pharmaceutical used as opioid antagonist. A molecular imprinted polymer electrochemical sensor for simple and rapid detection of NLX was prepared through the modification of commercial available screen printed carbon electrode (SPCE). The SPCE was modified with multi-walled carbon nanotubes (MWCNT) by drop coating to increase the signal response and improve the sensitivity. The MIP preparation was carried out via in situ electropolymerization using 4-aminobenzoic acid (4-ABA) as functional monomer. The morphology of the obtained sensor was characterized by scanning electron microscopy (SEM). Several parameters controlling the preparation and performance of the MIP sensor were studied and optimized. The electrochemical behavior of NLX at MIP and control non-imprinted (NIP) sensor was evaluated by differential pulse voltammetry (DPV), demonstrating a better MIP response and the success of the imprinting. The proposed MIP/MWCNT/SPCE sensor showed a linear relationship between peak current intensity and NLX concentration in the range between 0.25 and 10.0 μM, with limits of detection (LOD) and quantification (LOQ) of 0.20 μM and 0.67 μM respectively. The repeatability and reproducibility were also tested with relative standard deviations (RSD) of 4.6 and 9.6% respectively. Moreover, the applicability of the method was successfully confirmed with detection of NLX in biological samples (urine and human serum). The sensor is promising to be used for screening NLX in point-of-care people with opioid overdose.
- Electrochemical sensing of ecstasy with electropolymerized molecularly imprinted poly(o-phenylenediamine) polymer on the surface of disposable screen-printed carbon electrodesPublication . Couto, Rosa A.S.; Costa, Séfora S.; Mounssef, Bassim; Pacheco, João; Fernandes, Eduarda; Carvalho, Félix; Rodrigues, Cecília M.P.; Delerue-Matos, Cristina; Braga, Ataualpa A.C.; Moreira Gonçalves, Luís; Quinaz, M. BeatrizThis study demonstrates the ability of an electrochemical sensor based on molecularly imprinted polymers (MIPs) to selectively quantify 3,4-methylenedioxymethamphetamine (MDMA), also known as ecstasy, in biological samples. The device was constructed using ortho-phenylenediamine (o-PD) as the MIP’s building monomer at the surface of a screen-printed carbon electrode (SPCE). The step-by-step construction of the SPCE-MIP sensor was characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Density functional theory (DFT) calculations and modelling were performed not only to understand template-monomer interaction but also to comprehend which possible polymer structure - linear or ramified poly(o-PD) – indeed interacts with the analyte. The prepared sensor worked by directly measuring the MDMA oxidation signal through square-wave voltammetry (SWV) after an incubation period of 10 min. Several parameters were optimized, such as the monomer/template ratio, the number of electropolymerization scanning cycles, and the incubation period, to obtain the best sensing efficiency. Optimized sensors exhibited suitable selectivity, repeatability (2.6%), reproducibility (7.7%) and up to one month of stable response. A linear range up to 0.2 mmol L−1 was found with an r2 of 0.9990 and a limit of detection (LOD) and quantification (LOQ) of 0.79 and 2.6 μmol L−1 (0.15 and 0.51 μg mL−1), respectively. The proposed sensor was successfully applied to human blood serum and urine samples, showing its potential for application in medicine and in forensic sciences.
- Molecularly imprinted electrochemical sensor for the point-of-care detection of a breast cancer biomarker (CA 15-3)Publication . Pacheco, João; Silva, Marta S.V.; Freitas, Maria; Nouws, Henri; Delerue-Matos, CristinaThe incidence of breast cancer has been increasing over the years. To control and monitor this disease several tumor biomarkers have been proposed for early diagnosis, patient follow-up and/or treatment guidance. The only serum breast cancer biomarker in current use is the cancer antigen 15-3 (CA 15-3). In this work a molecularly imprinted polymer (MIP)-based electrochemical (voltammetric) sensor to monitor breast cancer was developed, based on direct surface imprinting of CA 15-3 on a screen-printed gold electrode (Au-SPE). The imprinting was performed in two steps: (1) adsorption of CA 15-3 on the surface of the Au-SPE and (2) electropolymerization of 2-aminophenol around the adsorbed protein. After extraction of the imprinted protein voltammetric analysis was conducted using hexacyanoferrate(II/III) as redox probe, measuring the signals before and after protein binding. The sensor was characterized by voltammetric techniques and electrochemical impedance spectroscopy, and the analytical responses of imprinted and non-imprinted polymer sensors were studied. A linear relationship between the peak current intensity of the redox probe and the logarithm of CA 15-3 concentration was established between 5 and 50 U mL−1, achieving a limit of detection of 1.5 U mL−1. The prepared MIP-sensor provides fast (15 min) analysis and is cheap, easy to prepare, disposable and could easily be integrated in small portable point-of care devices.
- Computational Modelling and Sustainable Synthesis of a Highly Selective Electrochemical MIP-Based Sensor for Citalopram DetectionPublication . Rebelo, Patrícia; Pacheco, João; Voroshylova, Iuliia V.; Seguro, Isabel; Cordeiro, Maria Natália D. S.; Delerue-Matos, CristinaA novel molecularly imprinted polymer (MIP) has been developed based on a simple and sustainable strategy for the selective determination of citalopram (CTL) using screen-printed carbon electrodes (SPCEs). The MIP layer was prepared by electrochemical in situ polymerization of the 3-amino-4 hydroxybenzoic acid (AHBA) functional monomer and CTL as a template molecule. To simulate the polymerization mixture and predict the most suitable ratio between the template and functional monomer, computational studies, namely molecular dynamics (MD) simulations, were carried out. During the experimental preparation process, essential parameters controlling the performance of the MIP sensor, including CTL:AHBA concentration, number of polymerization cycles, and square wave voltammetry (SWV) frequency were investigated and optimized. The electrochemical characteristics of the prepared MIP sensor were evaluated by both cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) techniques. Based on the optimal conditions, a linear electrochemical response of the sensor was obtained by SWV measurements from 0.1 to 1.25 µmol L−1 with a limit of detection (LOD) of 0.162 µmol L−1 (S/N = 3). Moreover, the MIP sensor revealed excellent CTL selectivity against very close analogues, as well as high imprinting factor of 22. Its applicability in spiked river water samples demonstrated its potential for adequate monitoring of CTL. This sensor offers a facile strategy to achieve portability while expressing a willingness to care for the environment
- Magnetic dispersive micro solid-phase extraction and gas chromatography determination of organophosphorus pesticides in strawberriesPublication . Fernandes, Virgínia Cruz; Freitas, Maria; Pacheco, João; Oliveira, José Maria; Domingues, Valentina; Delerue-Matos, CristinaMagnetic nanoparticles (MNPs) with different sizes and characteristics were synthesized to be used as a QuEChERS sorbents for the determination of seven organophosphorus pesticides (OPPs) in strawberries by gas chromatography analysis with flame photometric and mass spectrometry detection. To achieve the optimum conditions of modified QuEChERS procedure several parameters affecting the cleanup efficiency including the amount of the sorbents and cleanup time were investigated. The results were compared with classical QuEChERS methodologies and the modified QuEChERS procedure using MNPs showed the better performance. Under the optimum conditions of the new methodology, three spiking levels (25, 50 and 100 μg kg-1) were evaluated in a strawberry sample. The results showed that the average recovery was 93% and the relative standard deviation was less than 12%. The enrichment factor ranged from 111 to 145%. The good linearity with coefficients of determination of 0.9904-0.9991 was obtained over the range of 25-250 μg kg-1 for 7 OPPs. It was determined that the MNPs have an excellent function as sorbent when purified even using less amount of sorbents and the magnetic properties allowed non-use of the centrifugation in cleanup step. The new methodology was applied in strawberry samples from conventional and organic farming. The new sorbents were successfully applied for extraction and determination of OPPs in strawberries.