Ronaldo C. Faria

Electrochemical oxidation of o-aminophenol in aqueous acidic medium : formation of film and soluble products

The electrochemical oxidation of o-aminophenol (OAP) has been studied by cyclic voltammetry on platinum (Pt) and glassy carbon (GC) electrodes. Films formed on Pt exhibited a voltammetric response that is dependent on the final potential applied during the electropolymerization. Although a less electroactive film has been obtained on Pt electrodes cycled at higher potentials, modified GC electrodes showed a well-defined redox response independently of the potential range used. This result is attributed to an activation process of the GC electrode rather than to an electroactive film deposited on the electrode. The deposition process of thin films was also investigated with quartz crystal microbalance experiments. Poly-o-aminophenol (POAP) films were insoluble with an electrochromic response from colorless to brown, and a ladder structure confirmed by infrared spectra. Exhaustive electrolysis of OAP produced a reasonable amount of soluble product, which after solvent extraction, was characterized as 2-aminophenoxazin-3-one (APZ), a product also prepared by chemical oxidation of OAP. A route of electrooxidation of OAP has been proposed based on electrochemical and spectroscopic results.

Electrochemical detection of Salmonella using gold nanoparticles.

A disposable immunosensor for Salmonella enterica subsp. enterica serovar Typhimurium LT2 (S) detection using a magneto-immunoassay and gold nanoparticles (AuNPs) as label for electrochemical detection is developed. The immunosensor is based on the use of a screen-printed carbon electrode (SPCE) that incorporates a permanent magnet underneath. Salmonella containing samples (i.e. skimmed milk) have been tested by using anti-Salmonella magnetic beads (MBs-pSAb) as capture phase and sandwiching afterwards with AuNPs modified antibodies (sSAb-AuNPs) detected using differential pulse voltammetry (DPV). A detection limit of 143 cells mL(-1) and a linear range from 10(3) to 10(6) cells mL(-1) of Salmonella was obtained, with a coefficient of variation of about 2.4%. Recoveries of the sensor by spiking skimmed milk with different quantities of Salmonella of about 83% and 94% for 1.5×10(3) and 1.5×10(5) cells mL(-1) were obtained, respectively. This AuNPs detection technology combined with magnetic field application reports a limit of detection lower than the conventional commercial method carried out for comparison purposes in skimmed milk samples.

A microfluidic electrochemiluminescent device for detecting cancer biomarker proteins

We describe an electrochemiluminescence (ECL) immunoarray incorporated into a prototype microfluidic device for highly sensitive protein detection and apply this system to accurate, sensitive measurements of prostate-specific antigen (PSA) and interleukin-6 (IL-6) in serum. The microfluidic system employed three molded polydimethylsiloxane (PDMS) channels on a conductive pyrolytic graphite chip (2.5u2009×u20092.5xa0cm) inserted into a machined chamber and interfaced with a pump, switching valve, and sample injector. Each of the three PDMS channels encompasses three 3xa0μL analytical wells. Capture-antibody-decorated single-wall carbon nanotube forests are fabricated in the bottom of the wells. The antigen is captured by these antibodies on the well bottoms. Then, a RuBPY-silica-secondary antibody (Ab2) label is injected to bind to antigen on the array, followed by injection of sacrificial reductant tripropylamine (TPrA) to produce ECL. For detection, the chip is placed into an open-top ECL measuring cell, and the channels are in contact with electrolyte in the chamber. Potential applied at 0.95xa0V versus Ag/AgCl oxidizes TPrA to produce ECL by redox cycling the RuBPY species in the particles, and ECL light is measured by a charge-coupled device camera. This approach achieved ultralow detection limits of 100xa0fgu2009mL−1 for PSA (9xa0zeptomole) and 10xa0fgu2009mL−1 (1xa0zeptomole) for IL-6 in calf serum, a 10–25-fold improvement of a similar non-microfluidic array. PSA and IL-6 in synthetic cancer patient serum samples were detected in 1.1xa0h and results correlated well with single-protein enzyme-linked immunosorbent assays.

On-line protein capture on magnetic beads for ultrasensitive microfluidic immunoassays of cancer biomarkers.

Accurate, sensitive, multiplexed detection of biomarker proteins holds significant promise for personalized cancer diagnostics. Here we describe the incorporation of a novel on-line chamber to capture cancer biomarker proteins on magnetic beads derivatized with 300,000 enzyme labels and 40,000 antibodies into a modular microfluidic immunoarray. Capture and detection chambers are produced from PDMS on machined molds and do not require lithography. Protein analytes are captured from serum or other biological samples in the stirred capture chamber on the beads held in place magnetically. The beads are subsequently washed free of sample components, and wash solutions sent to waste. Removal of the magnet and valve switching sends the magnetic bead-protein bioconjugates into a detection chamber where they are captured on 8 antibody-decorated gold nanoparticle-film sensors and detected amperometrically. Most steps in the immunoassay including protein capture, washing and measurement are incorporated into the device. In simultaneous assays, the microfluidic system gave ultralow detection limits of 5 fg mL(-1) for interleukin-6 (IL-6) and 7 fg mL(-1) for IL-8 in serum. Accuracy was demonstrated by measuring IL-6 and IL-8 in conditioned media from oral cancer cell lines and showing good correlations with standard ELISAs. The on-line capture chamber facilitates rapid, sensitive, repetitive protein separation and measurement in 30 min in a semi-automated system adaptable to multiplexed protein detection.

Automated Multiplexed ECL Immunoarrays for Cancer Biomarker Proteins

Point-of-care diagnostics based on multiplexed protein measurements face challenges of simple, automated, low-cost, and high-throughput operation with high sensitivity. Herein, we describe an automated, microprocessor-controlled microfluidic immunoarray for simultaneous multiplexed detection of small protein panels in complex samples. A microfluidic sample/reagent delivery cassette was coupled to a 30-microwell detection array to achieve sensitive detection of four prostate cancer biomarker proteins in serum. The proteins are prostate specific antigen (PSA), prostate specific membrane antigen (PSMA), platelet factor-4 (PF-4), and interlukin-6 (IL-6). The six channel system is driven by integrated micropumps controlled by an inexpensive programmable microprocessor. The reagent delivery cassette and detection array feature channels made by precision-cut 0.8 mm silicone gaskets. Single-wall carbon nanotube forests were grown in printed microwells on a pyrolytic graphite detection chip and decorated with capture antibodies. The detection chip is housed in a machined microfluidic chamber with a steel metal shim counter electrode and Ag/AgCl reference electrode for electrochemiluminescent (ECL) measurements. The preloaded sample/reagent cassette automatically delivers samples, wash buffers, and ECL RuBPY-silica-antibody detection nanoparticles sequentially. An onboard microcontroller controls micropumps and reagent flow to the detection chamber according to a preset program. Detection employs tripropylamine, a sacrificial reductant, while applying 0.95 V vs Ag/AgCl. Resulting ECL light was measured by a CCD camera. Ultralow detection limits of 10-100 fg mL(-1) were achieved in simultaneous detection of the four protein in 36 min assays. Results for the four proteins in prostate cancer patient serum gave excellent correlation with those from single-protein ELISA.

3D-printed supercapacitor-powered electrochemiluminescent protein immunoarray.

Herein we report a low cost, sensitive, supercapacitor-powered electrochemiluminescent (ECL) protein immunoarray fabricated by an inexpensive 3-dimensional (3D) printer. The immunosensor detects three cancer biomarker proteins in serum within 35 min. The 3D-printed device employs hand screen printed carbon sensors with gravity flow for sample/reagent delivery and washing. Prostate cancer biomarker proteins, prostate specific antigen (PSA), prostate specific membrane antigen (PSMA) and platelet factor-4 (PF-4) in serum were captured on the antibody-coated carbon sensors followed by delivery of detection-antibody-coated Ru(bpy)3(2+) (RuBPY)-doped silica nanoparticles in a sandwich immunoassay. ECL light was initiated from RuBPY in the silica nanoparticles by electrochemical oxidation with tripropylamine (TPrA) co-reactant using supercapacitor power and ECL was captured with a CCD camera. The supercapacitor was rapidly photo-recharged between assays using an inexpensive solar cell. Detection limits were 300-500f gmL(-1) for the 3 proteins in undiluted calf serum. Assays of 6 prostate cancer patient serum samples gave good correlation with conventional single protein ELISAs. This technology could provide sensitive onsite cancer diagnostic tests in resource-limited settings with the need for only moderate-level training.

Electrochromic properties of lithium doped WO3 films prepared by the sol-gel process

Abstract The electrochemical responses of amorphous thin films of lithium doped tungsten trioxide (Li x WO 3 ) prepared by the sol–gel method were studied. The electrode mass change in the oxide films during cyclic voltammetry and chronoamperometry measurements was evaluated with electrochemical quartz crystal microbalance (EQCM). The electrode mass change and electrochemical performances depend on the lithium doping level. Higher lithium doping levels lead to better electrochemical performances and to higher electrode mass changes in the insertion–deinsertion process. The electrochromic properties of the films investigated in situ using a spectroelectrochemical method are in agreement with EQCM measurements. The bleaching process in the lithium doped film was complete whereas in pure WO 3 films a residual coloration was observed.

Electrocatalytic Oxidation and Voltammetric Determination of Hydrazine in Industrial Boiler Feed Water Using a Cobalt Phthalocyanine-modified Electrode

Abstract A carbon paste electrode modified with cobalt phthalocyanine (CPECoPc) was developed and applied to the determination of hydrazine [N2H4] in industrial boiler feed water. The CPECoPc exhibited good electrocatalytical activity for hydrazine oxidation at pH 13. A linear correlation was obtained between anodic peak current (Iap) and hydrazine concentration in the range of 1.25 × 10−4 to 9.80 × 10−4 mol L−1, fit by the equation Iap = 1.47 + 4.90 × 105 [N2H4] with a correlation coefficient of 0.9967. A detection limit of 7.35 × 10−5 mol L−1 was obtained. Recovery of hydrazine from three samples ranged between 99.0% and 102.9%. The modified electrode showed no interference by cations commonly present in boiler water, such as K+, Na+, Ca2+, Mg2+, Al3+, Pb2+, and Zn2+. The results obtained for hydrazine in boiler water using the proposed modified electrode are in agreement with the data obtained by a standard spectrophotometric method, at the 95% confidence level.

Electrochemical determination of estradiol using a thin film containing reduced graphene oxide and dihexadecylphosphate

Graphene is a material that has attracted attention with regard to sensing and biosensing applications in recent years. Here, we report a novel treatment (using ultrasonic bath and ultrasonic tip) to obtain graphene oxide (GO) and a new stable conducting film using reduced graphene oxide (RGO) and dihexadecylphosphate film (DHP). The GO was obtained by chemical exfoliation and it was reduced using NaBH4. Subsequently, RGO-DHP dispersion was prepared and it was dropped onto a glassy carbon electrode by casting technique. The electrode was characterized by cyclic voltammetry and electrochemical spectroscopy impedance. The voltammetric behavior of the RGO-DHP/GC electrode in the presence of estradiol was studied, and the results reported an irreversible oxidation peak current at 0.6V. Under the optimal experimental conditions, using linear sweep adsorptive stripping voltammetry, the detection limit obtained for this hormone was 7.7×10(-8)mol L(-1). The proposed electrode can be attractive for applications as electrochemical sensors and biosensors.

Rapid Microfluidic Immunoassays of Cancer Biomarker Proteins Using Disposable Inkjet-Printed Gold Nanoparticle Arrays

Conventional protein detection methods such as enzyme-linked immunosorbent assays (ELISA) often take many hours to complete and usually only apply to one protein at a time. More rapid, multiplexed methods are needed for point-of-care (POC) and surgical applications in future personalized cancer diagnostics and therapy. This paper describes a low-cost inkjet-printed gold nanoparticle (AuNP) sensor chip integrated into a simple microfluidic immunoarray to achieve detection of two cancer biomarker proteins in 5 μL samples in 8 min. Magnetic beads of 1 μm diameter derivatized with ∼300 000 enzyme labels and thousands of antibodies were used to capture the biomarker proteins from samples. The beads with captured proteins are then injected into the microfluidic system and captured by antibodies on nanostructured sensor elements to provide high sensitivity and ultralow detection limits (DL). For assay times of 45 mins, DLs were 78 fg mL−1 for interleukin-6 (IL-6) and 19 fg mL−1 for interleukin-8 (IL-8). Decreasing assay time to 8 min provided clinically relevant DLs of 5 pg mL−1. Accuracy was demonstrated by determining IL-6 and IL-8 in conditioned media from head and neck squamous cell carcinoma (HNSCC) cells and comparing results to those from standard single-protein ELISAs. Results suggest that this device can be employed for rapid detection of a wide range of disease-related proteins in clinical applications.