Incorporating electronic tongues into microfluidic devices brings benefits as dealing with small amounts of sample/discharge. Nonetheless, such measurements may be time-consuming in some applications ...once they require several operational steps. Here, we designed four collinear electrodes on a single printed circuit board, further comprised inside a straight microchannel, culminating in a robust e-tongue device for faster data acquisition. An analog multiplexing circuit automated the signal’s routing from each of the four sensing units to an impedance analyzer. Both instruments and a syringe pump are controlled by dedicated software. The automated e-tongue was tested with four Brazilian brands of liquid sucralose-based sweeteners under 20 different flow rates, aiming to systematically evaluate the influence of the flow rate in the discrimination among sweet tastes sold as the same food product. All four brands were successfully distinguished using principal component analysis of the raw data, and despite the nearly identical sucralose-based taste in all samples, all brands’ significant distinction is attributed to small differences in the ingredients and manufacturing processes to deliver the final food product. The increasing flow rate improves the analyte’s discrimination, as the silhouette coefficient reaches a plateau at ~3 mL/h. We used an equivalent circuit model to evaluate the raw data, finding a decrease in the double-layer capacitance proportional to improvements in the samples’ discrimination. In other words, the flow rate increase mitigates the formation of the double-layer, resulting in faster stabilization and better repeatability in the sensor response.
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•Sensitive detection and discrimination of four classes of pesticides.•Set of three glove-embedded sensors printed on three fingers of a rubber glove.•High performance detection of ...carbendazim, diuron, paraquat and fenitrothion.•Pesticides can be detected in real samples of apple, cabbage and in orange juice.•Simply touching with the fingers was demonstrated with multidimensional projections.
On-site monitoring of pesticides in food, water and in the environment is crucial for human health, and this requires low cost, portable devices for widespread deployment of the technology. In this paper, we report on selective, sensitive detection and discrimination of four classes of pesticides, namely carbendazim (carbamate), diuron (phenylamide), paraquat (bipyridinium) and fenitrothion (organophosphate), using a set of three glove-embedded sensors printed on three fingers of a rubber glove. The sensors consisted of a pre-treated screen-printed carbon electrode and two other such electrodes coated with either carbon spherical shells (CSS) or Printex carbon nanoballs (PCNB). Detection of carbendazim and diuron was performed using differential pulse voltammetry (DPV) and the electrodes coated with CSS and PCNB, respectively, with limits of detection of 4.7 × 10–8 and 9.2 × 10–7 mol L–1. Square wave voltammetry (SWV) was applied to detect paraquat and fenitrothion with limits of detection 2.4 × 10–8 and 6.4 × 10–7 mol L–1 using the pretreated electrode in sulfuric acid solution. The high performance and discrimination of the pesticides at distinct concentrations in real samples of apple and cabbage by simply touching with the glove, and in orange juice by immersing the fingers was demonstrated with multidimensional projections. The sensors were robust against flexion in multiple times, stable and had reproducible response with no interference from other pesticides. With their high selectivity, sensitivity, easy operation and rapid pesticide detection, these glove-embedded sensors may also be employed in on-site analysis of other chemical threats and be extended to environmental and water samples.
DNA methylation is involved in the oncogenesis of head and neck squamous cell carcinoma and could be used for early detection of cancer to increase the chances of cure, but unfortunately diagnosis is ...usually made at late stages of the disease. In this work we developed genosensors to detect DNA methylation of the MGMT gene in head and neck cancer cell lines. The probe for MGMT promoter methylation was immobilized on gold electrodes modified with 11-mercaptoundecanoic acid (11-MUA) self-assembled monolayers (SAM). Detection was performed with electrochemical impedance spectroscopy, with clear distinction between methylated and non-methylated DNA from head and neck cell lines. The genosensor is sensitive with a low detection limit of 0.24 × 10−12 mol L−1. In addition, the cell lines FaDu, JHU28 and SCC25 for the MGMT gene, could be distinguished from the HN13 cell line which has a high degree of MGMT methylation (97%), thus confirming the selectivity. Samples with different percentages of MGMT DNA methylation could be separated in multidimensional projections using the visualization technique interactive document mapping (IDMAP). The genosensor matrix and the immobilization procedures are generic, and can be extended to other DNA methylation biomarkers.
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•Electrochemical genosensors to detect DNA methylation of the MGMT gene in head and neck cancer cell lines.•Gold electrodes functionalized with self-assembled monolayers of acid mercaptoundecanoic (MUA).•Detection limit was of 6.4 pM.
Nanostructured microelectrodes (NMEs) are an attractive alternative to yield sensitive bioassays in unprocessed samples. However, although valuable for different applications, nanoporous NMEs usually ...cannot boost the sensitivity of diffusion-limited analyses because of the enlarged Debye length within the nanopores, which reduces their accessibility. To circumvent this limitation, nanopore-free gold NMEs were electrodeposited from 45 μm SU-8 apertures, featuring nanoridged microspikes on a recessed surface of gold thin film while carrying interconnected crown-like and spiky structures along the edge of a SU-8 passivation layer. These structures were grown onto ultradense, vertical array chips that offer a promising strategy for translating reproducible, high-resolution, and cost-effective sensors into real-world applications. The NMEs yielded reproducible analyses, while machine learning allowed us to predict the analytical responses from NME electrodeposition data. By taking advantage of the high surface area and accessible structure of the NMEs, these structures provided a sensitivity for Fe(CN)
that was 5.5× higher than that of bare WEs while also delivering a moderate antibiofouling property in undiluted human plasma. As a proof of concept, these electrodes were applied toward the fast (22 min) and simple determination of
by monitoring the oxidation of Fe(CN)
, which acted as a cellular respiration rate redox reporter. The sensors also showed a wide dynamic range, spanning 5 orders of magnitude, and a calculated limit of detection of 0.2 CFU mL
.
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•Nanostructured film of clay and nickel phthalocyanine was assembled by the LbL technique.•Electrochemical sensor detects DA in the presence of common interferents.•A synergistic ...effect in the LbL film in a quadri-layer assembly was verified.•The sensor exhibited a low LOD (1.0 μmol L−1) and a linear range 5–150 μmol L−1.
Dopamine (DA) abnormal levels are related to diseases which makes important the development of fast, reliable, low-cost and sensitive devices for diagnosis and pharmaceutical controls. Nanostructured film composite of sodium montmorillonite clay (Na+MMT) and nickel phthalocyanine (NiTsPc) was self-assembled by layer-by-layer (LbL) technique and applied as electrochemical sensor for DA in the presence of common natural interferents as ascorbic acid (AA) and uric acid (UA). Three different LbL architecture films were investigated: LbL films of clay (PEI/Na+MMT) and phthalocyanine (PEI/NiTsPc) in a bilayer structure with a conventional polyelectrolyte (PEI) and a composite film formed by both materials to verify the synergistic effect in the LbL film in a quadri-layer assembly (PEI/Na+MMT/PEI/NiTsPc). Structural characterization indicated molecular level interactions between the layers forming the LbL films. The ITO/(PEI/Na+MMT/PEI/NiTsPc)10 electrode exhibited a LOD of 1.0 μmol L−1 and linear range 5–150 μmol L−1.
The detection of pollutant traces in the public water supply and aquifers is essential for the safety of the population. In this article, we demonstrate that a simple electrochemical procedure in ...acidic solution can be employed for enhancing the sensitivity of flexible screen-printed carbon electrodes (SPEs) to detect bisphenol-A (BPA), hydroquinone, and catechol, simultaneously. The SPEs were pretreated electrochemically in a H2SO4 solution, which did not affect their morphology, yielding high current signals with well separated oxidation peaks. The sensitivity values were 0.28, 0.230, and 0.056 µA L µmol−1 with detection limits of 0.12, 0.82, and 0.95 µmol L−1 for hydroquinone, catechol, and BPA, respectively. The sensors were reproducible and selective for detecting BPA in plastic cups, and with adequate specificity not to be affected by interferents from water samples. The simple, inexpensive, and flexible SPE may thus be used to detect emerging pollutants and monitor the water quality.
•Cellulose nanowhiskers, silver nanoparticles and electrospun nanofibers were combined to produce ternary nanocomposites.•E-tongue sensing units were designed using ternary nanomposites.•Feature ...selection procedure using e-tongue data allowed the discrimination of distinct heavy metal solutions.•Aqueous solutions containing lead could be classified down to nanomolar concentration.
Contamination of water resources with heavy metal ions raises concerns because of their capability to accumulate in living organisms and cause serious health problems. As a consequence, the development of sensitive and reliable sensors capable to provide fast and accessible analysis of water quality regarding heavy metals is highly keen. Nanomaterials advancements have provided considerable improvements in these sensors, enabling efficient detection of different water pollutants even at extremely low concentration. In this work, we evaluated the performance of ternary nanocomposites based on electrospun nanofibers, cellulose nanowhiskers (CNW) and silver nanoparticles as sensing layers used in the electrical detection of heavy metals. These three materials were distinctly combined, resulting in six different sensors, which were arranged to compose an impedimetric electronic tongue. The synergism between the components could be verified by the enhancement of bulk conductance ability when CNW:Ag was combined with electrospun nanofibers. Adjustments of sensors and frequencies enabled efficient discrimination of distinct heavy metal ions. Moreover, the sensor array could distinguish pure water from aqueous solution contaminated with Pb2+ at concentrations as low as of 10 nmol L−1.
Lanthanide-doped upconversion nanoparticles (UCNPs) absorb low-energy photons, in the near-infrared region (NIR), and emit high-energy photons, in the visible or ultraviolet region (UV/Vis). The ...higher energy radiation emissions can be used to promote plasmonic photocatalytic reactions by coupling UCNPs with plasmonic nanoparticles. Thus, in this work, highly crystalline β-NaYF4:Yb3+,Er3+@NaYF4:Nd3+@NaYF4 UCNPs capped with an amino-modified nanosized silica shell were coupled with Au nanospheres (13 ± 2 nm). The plasmonic-driven dimerization of 4-aminothiophenol (4-ATP) to 4,4′-dimercaptoazobenzene (DMAB) was carried out solely by using the UCNP visible emissions to excite the Au nanoparticle localized surface plasmon resonance band. The reaction was monitored in situ through surface-enhanced Raman spectroscopy (SERS) and optimal conditions were achieved in order to eliminate secondary influences during spectra acquisition. The SERS substrates containing either UCNPs@SiO2-NH2/Au or SiO2-NH2/Au nanoparticles were prepared by the drop-cast method in silicon substrates. In the studied reaction conditions, plasmonic photocatalytic activity was observed only in the substrates containing UCNPs and Au nanoparticles. The plasmonic-driven reaction was achieved by UCNPs excitation with a 980 nm laser (25.7 mW), aligned in a Raman spectrometer, only after 5 s of exposition. Interactive document mapping (IDMAP), which is an unsupervised pattern recognition method, was applied to analyze the numerous SERS spectra acquired during the plasmonic photocatalytic measurements. The high values found for the silhouette coefficient (0.88 for the Si_SiO2-NH2/Au and 0.76 for the Si_NYF@SiO2-NH/Au substrate) indicate that strong discrimination among the Raman spectra was achieved. Thus, through IDMAP, it was observed that the SERS spectra obtained for the substrates containing either UCNPs@SiO2-NH2/Au or SiO2-NH2/Au corresponded to spectral features, respectively, from the DMAB product and the 4-ATP reagent, evidencing that, in the optimized reaction conditions, the dimerization occurred only through the interaction of the UCNPs with the Au nanospheres.
Diagnosis of cancer using electroanalytical methods can be achieved at low cost and in rapid assays, but this may require the combination with data treatment for determining biomarkers in real ...samples. In this paper, we report an immunomagnetic nanoparticle-based microfluidic sensor (INμ-SPCE) for the amperometric detection of the prostate-specific antigen (PSA) biomarker, the data of which were treated with information visualization methods. The INμ-SPCE consists of eight working electrodes, reference and counter electrodes. On the working electrodes, magnetic nanoparticles with secondary antibodies with the enzyme horseradish peroxidase were immobilized for the indirect detection of PSA in a sandwich-type procedure. Under optimal conditions, the immunosensor could operate within a wide range from 12.5 to 1111 fg·L
−1
, with a low detection limit of 0.062 fg·L
−1
. Multidimensional projections combined with feature selection allowed for the distinction of cell lysates with different levels of PSA, in agreement with results from the traditional enzyme-linked immunosorbent assay. The approaches for immunoassays and data processing are generic, and therefore the strategies described here may provide a simple platform for clinical diagnosis of cancers and other types of diseases.
Neuromyelitis optica spectrum disorder (NMOSD) is an inflammatory and autoimmune disease whose biomarker is the anti-AQP4-IgG autoantibody that binds to aquaporin-4 (AQP4) protein. We introduced a ...nanosensor with a sensitivity of 84.6%, higher than the CBA's 76.5%. Using silver nanoparticles (AgNPs), we detected not only seropositive but also some false-negative patients previously classified with CBA. It consisted of AgNPs coated with one of a panel of 5 AQP4 epitopes. The ability in detecting the anti-AQP4-IgG in NMOSD patients depended on the epitope and synergy could be obtained by combining different epitopes. We demonstrated that NMOSD patients could easily be distinguished from healthy subjects and patients with multiple sclerosis. Using the most sensitive AQP461-70 peptide, we established a calibration curve to estimate the concentration of anti-AQP4-IgG in seropositive NMOSD patients. The ability to enhance the accuracy of the diagnosis may improve the prognosis of 10-27% of anti-AQP4-IgG seronegative patients worldwide.
Schematic diagram of the interaction mechanism of the AQP4-peptide conjugated AgNPs with IgG samples. When a serum sample containing the anti-AQP4-IgG is added to the AgNPs suspension, the target antibody promotes nanoparticle aggregation, evidenced by color changing from yellow to orange-red variations, associated with the appearance of new LSPR bands in the UV–vis absorption spectrum, at longer wavelengths and 360 nm. The maintenance of suspension original color (yellow) and one single LSPR band characterize the non-specific response of the AQP4-peptide conjugated AgNPs after interaction with serum samples without the anti-AQP4-IgG autoantibody. Display omitted
•Prognosis of AQP4-IgG CBA seronegative patients may be improved with our approach.•AQP4-IgG detection was reached with a low-cost nanoparticle colorimetric method.•High accuracy was reached with a judicious choice of AQP4 target epitopes.•AQP4 epitope targets differ in patients with distinct clinical diagnosis of NMOSD.
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