Graphene and CdS nanocomposite: A facile interface for construction of DNA-based electrochemical biosensor and its application to the determination of phenformin

A sandwich-type photoelectrochemical aptasensor using Au/BiVO4 and CdS quantum dots for carcinoembryonic antigen assay

A novel sandwich-type photoelectrochemical (PEC) aptasensor for the carcinoembryonic antigen (CEA) assay was fabricated using the CEA aptamer, Au/BiVO₄ and CdS quantum dots (CdS QDs). In virtue of the localized surface plasmon resonance effect of Au nanoparticles, Au/BiVO₄ showed an effective utilization of visible light and excellent photoactivity, and was employed as the photoanode. After CdS QDs were conjugated to Au/BiVO₄ through the sandwich structure based on the hybridization of the CEA aptamer with two partially complementary single-stranded DNA molecules, the photocurrents were further enhanced by a resonance energy transfer between CdS QDs and Au nanoparticles. Meanwhile, the consumption of the photo-induced holes by ascorbic acid could also retard the combination of the electron-hole pairs and cause an increase of the photocurrents. However, the specific recognition of CEA by the CEA aptamer could destroy the sandwich structure and remarkably weaken the photocurrent response. Thus, the quantitative detection of CEA was connected with the decrease of the photocurrent. Benefitting from the above methods for signal enhancement, the PEC aptasensor showed a wide sensing range of 0.0001-10 ng mL^-1 and a low detection limit of 0.047 pg mL^-1 for CEA detection. The specificity, stability and recoveries of the PEC aptasensor were also excellent. Therefore, the construction of the present PEC aptasensor provides a universal and practical method for sensing other substances.

Synthesis of a CdS-decorated Eu-MOF nanocomposite for the construction of a self-powered photoelectrochemical aptasensor

A composite of CdS nanoparticles and a europium metal organic framework (Eu-MOF) (CdS/Eu-MOF) was synthesized. The unique properties of MOFs help to improve the photoelectrochemical (PEC) properties of CdS by reducing charge carrier recombination and utilizing a broader spectrum for light harvesting. Under visible light illumination, the photocurrent of the CdS/Eu-MOF composite modified electrode was about 2.5-fold higher than that of the CdS modified electrode. When an ampicillin (AMP)-binding aptamer was immobilized on the CdS/Eu-MOF modified electrode as a recognition element, a self-powered PEC aptasensor exhibiting a specific photocurrent response to AMP was constructed. Several experimental conditions such as the ratio of CdS to MOF, the coating amount of the CdS/Eu-MOF suspension and the concentration of the aptamer were studied. Under optimum conditions, the photocurrent of the developed sensor was linearly related to the logarithm AMP concentration in the range of 1 × 10-10 to 2 × 10-7 M, with a detection limit (3S/N) of 9.3 × 10-11 M. Moreover, this sensor exhibited excellent selectivity, good repeatability and desirable stability. It was successfully applied to the detection of AMP in lake water and milk samples.

Graphene-based biosensors for the detection of prostate cancer protein biomarkers: a review

Prostate cancer (PC) is the sixth most common cancer type in the world, which causes approximately 10% of total cancer fatalities. The detection of protein biomarkers in body fluids is the key topic for the diagnosis and prognosis of PC. Highly sensitive screening of PC is the most effective approach for reducing mortality. Thus, there are a growing number of literature that recognizes the importance of new technologies for early diagnosis of PC. Graphene is playing an important role in the biosensor field with remarkable physical, optical, electrochemical and magnetic properties. Many recent studies demonstrated the potential of graphene materials for sensitive detection of protein biomarkers. In this review, the graphene-based biosensors toward PC analysis are mainly discussed in two groups: Firstly, novel biosensor interfaces were constructed through the modification of graphene materials onto sensor surfaces. Secondly, ingenious signal amplification strategies were developed using graphene materials as catalysts or carriers. Graphene-based biosensors have exhibited remarkable performance with high sensitivities, wide detection ranges, and long-term stabilities.

One-pot synthesis of a CdS-reduced graphene oxide-carbon nitride composite for self-powered photoelectrochemical aptasensing of PCB72

Graphitic carbon nitride (C3N4) is a carbon-based metal-free semiconductor, which has been widely explored as a photoactive material. In this work, the CdS, reduced graphene oxide (rGO) and C3N4 (CdS-rGO-C3N4) composite was synthesized by a simple one-pot hydrothermal method and utilized to construct a photoelectrochemical (PEC) sensor. Compared with CdS, C3N4 and CdS-C3N4, the CdS-rGO-C3N4 composite exhibited enhanced photoelectrochemical (PEC) performance, due to the expanded absorption of C3N4 in the visible region by CdS and promoted the charge carrier separation of a photoelectrode by rGO. Based on a glassy carbon electrode (GCE) modified with CdS-rGO-C3N4 and a PCB72-binding aptamer (ap/CdS-rGO-C3N4/GCE), a PEC aptasensor for the detection of 2,3',5,5'-tetrachlorobiphenyl (PCB72) was developed. When H2O2 was added into the electrolyte, the PEC sensor exhibited an amplified response toward PCB72, and could be operated in a self-powered mode at a potential of 0 V. Under optimum conditions, the constructed PEC aptasensor exhibited a wide linear range of 10 to 1000 ng mL-1 for PCB72 detection, with a low detection limit (S/N = 3) of 1.0 ng mL-1. Moreover, this aptasensor exhibited high selectivity, good reproducibility and high stability. The applicability of the developed PEC strategy was demonstrated by determining PCB72 in environmental water.

Graphitic Carbon Nitride Sensitized with CdS Quantum Dots for Visible-Light-Driven Photoelectrochemical Aptasensing of Tetracycline

Graphitic carbon nitride (g-C₃N₄) is a new type of metal-free semiconducting material with promising applications in photocatalytic and photoelectrochemical (PEC) devices. In the present work, g-C₃N₄ coupled with CdS quantum dots (QDs) was synthesized and served as highly efficient photoactive species in a PEC sensor. The surface morphological analysis showed that CdS QDs with a size of ca. 4 nm were grafted on the surface of g-C₃N₄ with closely contacted interfaces. The UV-visible diffuse reflection spectra (DRS) indicated that the absorption of g-C₃N₄ in the visible region was enhanced by CdS QDs. As a result, g-C₃N₄-CdS nanocomposites demonstrated higher PEC activity as compared with either pristine g-C₃N₄ or CdS QDs. When g-C₃N₄-CdS nanocomposites were utilized as transducer and tetracycline (TET)-binding aptamer was immobilized as biorecognition element, a visible light-driven PEC aptasensing platform for TET determination was readily fabricated. The sensor showed a linear PEC response to TET in the concentration range from 10 to 250 nM with a detection limit (3S/N) of 5.3 nM. Thus, g-C₃N₄ sensitized with CdS QDs was successfully demonstrated as useful photoactive nanomaterials for developing a highly sensitive and selective PEC aptasensor.

Determination of phenformin hydrochloride employing a sensitive fluorescent probe

A complexation of non-fluorescent phenformin hydrochloride (PFH) with cucurbit [7]uril (CB [7]) in aqueous solution was investigated using the fluorescent probe of palmatine (PAL) coupled with CB [7]. The fluorescent probe of CB [7]-PAL exhibited strong fluorescence in aqueous solution, which was quenched gradually with the increase of PFH. This effect is observed because when PFH was added to the host-guest system of CB [7]-PAL, PFH and PAL competed to occupy the CB [7] cavity. Portions of the PAL molecule were expelled from the CB [7] cavity owing to the introduction of PFH. Based on the significant quenching of the supramolecular complex fluorescence intensity, a fluorescence method of high sensitivity and selectivity was developed to determine PFH with good precision and accuracy for the first time. The linear range of the method was 0.005-1.9 μg mL(-1) with a detection limit of 0.003 μg mL(-1). In this work, association constants (K) of PFH with CB [7] were also determined. KCB [7]-PFH=(2.52±0.05)×10(5) L mol(-1). The ability of PFH to bind with CB [7] is stronger than that of PAL. The results of a density functional theory calculation authenticated that the moiety of PFH was embedded in the hydrophobic cavity of CB [7] tightly, and the nitrogen atom is located in the vicinity of a carbonyl-laced portal in the energy-minimized structure. The molecular modelling of the interaction between PFH and CB [7] was also confirmed by (1)H NMR spectra (Bruker 600 MHz).

Engineered Carbon-Nanomaterial-Based Electrochemical Sensors for Biomolecules

The study of electrochemical behavior of bioactive molecules has become one of the most rapidly developing scientific fields. Biotechnology and biomedical engineering fields have a vested interest in constructing more precise and accurate voltammetric/amperometric biosensors. One rapidly growing area of biosensor design involves incorporation of carbon-based nanomaterials in working electrodes, such as one-dimensional carbon nanotubes, two-dimensional graphene, and graphene oxide. In this review article, we give a brief overview describing the voltammetric techniques and how these techniques are applied in biosensing, as well as the details surrounding important biosensing concepts of sensitivity and limits of detection. Building on these important concepts, we show how the sensitivity and limit of detection can be tuned by including carbon-based nanomaterials in the fabrication of biosensors. The sensing of biomolecules including glucose, dopamine, proteins, enzymes, uric acid, DNA, RNA, and H2O2 traditionally employs enzymes in detection; however, these enzymes denature easily, and as such, enzymeless methods are highly desired. Here we draw an important distinction between enzymeless and enzyme-containing carbon-nanomaterial-based biosensors. The review ends with an outlook of future concepts that can be employed in biosensor fabrication, as well as limitations of already proposed materials and how such sensing can be enhanced. As such, this review can act as a roadmap to guide researchers toward concepts that can be employed in the design of next generation biosensors, while also highlighting the current advancements in the field.

Electrochemical detection of a pathogenic Escherichia coli specific DNA sequence based on a graphene oxide–chitosan composite decorated with nickel ferrite nanoparticles

An electrochemical genosensor has been fabricated forEscherichia coliO157:H7 detection using a graphene oxide–nickel ferrite–chitosan nanocomposite electrophoretically deposited on an ITO coated glass substrate.

Biogenic gold nanoparticles-reduced graphene oxide nanohybrid: synthesis, characterization and application in chemical and biological reduction of nitroaromatics

The biogenic AuNPs/rGO can participate in and accelerate electron transfer, and catalyze both chemical and biological reduction of nitroaromatics efficiently.