Label-free Photoelectrochemical Aptasensor Research Articles

High affinity aptamers for ultra-sensitive detection of aflatoxin B1 in milk and groundnut samples with label-free photo-electrochemical aptasensor

Aflatoxin B1 is a potent liver toxin and easily accumulated in foodstuff and environment via the food chain, subjecting high hazards to human health. Rapid initial diagnosis is one of the most impressive monitoring procedures to overcome the potential hazards. Nevertheless, the classical approaches confront many limitations, like low specificity and sensitivity and complicated procedures. Herein, a photo-electrochemical aptasensor based on sensitized poly(dopamine)@functionalized multiwall carbon nanotube/titanium dioxide (PDA@f-MWCNTs/TiO2 NTs) was designed to detect aflatoxin B1 in real samples (e.g. groundnut and milk). The mentioned label-free biosensing platform not only needed simple operations but also presented outstanding reusability, storage stability, reproducibility, and specificity simultaneously. This suggested strategy could sensitively and selectively detect aflatoxin B1 with dynamic range of 0.005–50 ng/mL and a low limit of detection 1 pg/mL. This procedure could provide the bright prospect for detection of aflatoxin B1 residues in foodstuff.

An ultrasensitive label-free photoelectrochemical aptasensor based on terminal deoxynucleotidyl transferase amplification and catalytic reaction of G-quadruplex/hemin

An ultrasensitive photoelectrochemical (PEC) analysis method based on terminal deoxynucleotidyl transferase (TdT) amplification effect and G-quadruplex/hemin (G4/hemin) catalytic reaction assisted signal amplification was prepared for the determination of ampicillin. A novel Au NPs@SnIn4S8-graphene sensitized structure was used as photoactive material to attain an intense basic photocurrent. In the presence of the target, P1 obtained by strand displacement reaction was introduced into the electrode surface, and abundant G4/hemin was formed in the presence of TdT and hemin. Subsequently, G4/hemin with horseradish peroxidase-mimicking activity catalyzed the oxidation of 4-chloro-1-naphthol by H2O2 to form benzo-4-chlorohexadienone precipitation on the modified electrode surface, which severely hindered the electron transfer and effectively inhibited the photocurrent output. The detection range of the PEC aptasensor for ampicillin was 10 fM-30 nM, and the limit of detection was 4.97 fM. The aptasensor had good stability and high sensitivity, and possessed a promising application in biological analysis and environmental monitoring.

A sensitive label-free photoelectrochemical aptasensor based on a novel PTB7-Th/H2O2 system with unexpected photoelectric performance for C-reactive protein analysis

Herein, a sensitive label-free photoelectrochemical (PEC) aptasensor was constructed for C-reactive protein (CRP) analysis based on a novel and efficient poly{4,8-bis[5-(2-ethylhexyl) thiophen-2-yl]benzo[1,2-b:4,5-b′]dithiophene-2,6-diyl-alt-3-fluoro-2-[(2-ethylhexyl)carbonyl] thieno[3,4-b]-thiophene-4,6-diyl} (PTB7-Th)/H2O2 system with unexpected photoelectric performance. The proposed PTB7-Th/H2O2 system without any sensitizer could surmount defect of the poor photoelectric conversion efficiency of PTB7-Th, leading to the unexpected 10-fold photocurrent enhancement compared to the common PTB7-Th/PBS system. The strong enhancement effect might originate from the special function of hydrogen peroxide (H2O2) towards PTB7-Th. On the one hand, H2O2 as electron acceptor could continuously capture photogenerated electrons located at acceptor part of PTB7-Th, which would visibly improve the charge separation efficiency of PTB7-Th and the electron-receiving property of electrolyte solution, thus leading to the obviously enhanced photoelectric conversion efficiency (PCE). More importantly, H2O2 as oxidant could oxidize PTB7-Th to obtain oxidation product of PTB7-Th (OPP) with carbonyl group and carboxyl group, and the electron cloud density in donor part of the OPP was higher than that of PTB7-Th, therefrom producing the stronger electron-donating property and higher photoelectrochemical (PEC) reaction efficiency. As a proof of concept, the proposed PTB7-Th/H2O2 system was successfully applied in the construction of a label-free PEC aptasensor for sensitive analysis of CRP, which performed a wide detection range from 1 pM to 1000 nM with a low detection limit of 0.33 pM. This study demonstrated a novel approach to the rational design of photoelectric conversion system with high PEC performance and provided an inspired tack for the construction of high-efficiency photoelectric devices.

A novel label-free photoelectrochemical aptasensor for the sensitive detection of ampicillin based on carbon-coated Bi2S3 nanorods

The prepared Bi2S3@C nanorods with remarkable photoelectrochemical properties served as a PEC sensor platform for the ultrasensitive analysis of ampicillin.

A simple label-free photoelectrochemical aptasensor for ultrasensitive detection of thrombin

This work demonstrates a label-free photoelectrochemical (PEC) aptamer sensor based on poly(5-formylindole)/Au (P5FIn/Au) nanocomposites for the ultrasensitive determination of thrombin (TB). As a photosensitive material, P5FIn exhibits excellent photocurrent response under visible light irradiation, and can capture more thrombin aptamers (TBA) due to large specific surface area and surface-rich aldehyde group. In addition, the aldehyde groups of P5FIn are conducive to the stable and efficient immobilization of aptamers or bioactive molecules, enhancing their biological activity. Au increases the absorption of visible light and effectively inhibits the recombination of photogenerated electron-hole pairs, thereby improving the photocurrent conversion efficiency of P5FIn. Therefore, after TB is specifically identified, the photocurrent decreases linearly. Under optimal conditions, this PEC aptasensor has a linear response ranging from 0.001 to 10 nM with detection limits as low as 0.2 pM. This sensor also has good selectivity, repeatability, stability and simple construction process. The determination results of TB in real human serum samples are also satisfactory, which will provide a practical PEC platform for the rapid detection of proteins in the future.

A label-free photoelectrochemical aptasensor for tetracycline based on Au/BiOI composites

Tetracycline (TC) as a broad-spectrum antibiotic arouses widespread concern in analytical chemistry field attributed to generation of the drug resistance and the damage to human body. Consequently, it is significant to develop a fast, sensitive and effective analysis method detecting TC. In this work, a photoelectrochemical (PEC) aptasensor was constructed to detect TC based on Au/BiOI composites. A one-pot synthetic route for Au/BiOI composites was proposed in ethylene glycol (EG) acted as reducing agent. Au nanoparticles (Au NPs) were conducive to achieving the effective utilization of light and electronic separation owing to the characteristics of strong light response and high conductivity. Furthermore, Au NPs on the Au/BiOI composites can form Au-S covalent bonding with sulfhydryl group at the aptamer terminal contributed to constructing a highly stable PEC aptasensor. The PEC aptasensor exhibited a wide linear range from 0.4 to 14,370 ng L−1 and down to the low detection limit 0.2 ng L−1 (S/N = 3). Moreover, the PEC aptasensor also showed good reproducibility and stability, expecting to be applied in actual environmental monitoring in future and expanding the application of Bi-based photoactive materials in analytical chemistry field.

A label-free photoelectrochemical aptasensor for facile and ultrasensitive mercury ion assay based on a solution-phase photoactive probe and exonuclease III-assisted amplification.

In typical photoelectrochemical (PEC) biosensing assays, electrodes are generally modified with photoactive probes and/or target recognition probes, which makes the processes complicated, time-consuming, and difficult to achieve excellent reproducibility. Hence, to overcome such shortcomings, we propose here an immobilization-free and label-free PEC aptasensor using solution-phase methylene blue (MB) as the PEC signal probe. Based on the unique T-Hg2+-T base pairs, and the diffusivity difference between free MB molecules and the MB/G-quadruplex composite towards the ITO electrode surface with negative charge, the "signal-off" approach for Hg2+ detection is developed. In the presence of target Hg2+, via the T-Hg2+-T bond formation, the two sticky ends of the hairpin DNA probe form a rigid duplex stem, which triggers the exonuclease III-facilitated target cycling amplification, and the formation of multiple G-quadruplexes. Upon the intercalation of MB in G-quadruplexes, significantly decreased photocurrent is obtained owing to the increased electrostatic repulsion between the MB/G-quadruplex composite and the ITO electrode. Therefore, highly sensitive and ultrasensitive Hg2+ determination is achieved, with a low detection limit of 1.2 pM, well below the maximum allowable Hg2+ level in drinking water defined by the WHO, China's Ministry of Health, and the US EPA. Due to the avoidance of sophisticated electrode modification and recognition probe immobilization processes, as well as an expensive labeling procedure, the PEC aptasensor proposed here demonstrates the advantages of simplicity, good reproducibility, rapidness and low cost.

Label-free photoelectrochemical aptasensor for tetracycline detection based on cerium doped CdS sensitized BiYWO6

A novel photoelectrochemical (PEC) aptasensor based on cerium (Ce) doped CdS modified graphene (G)/BiYWO6 was designed, which exhibits enhanced PEC intensity compared with pure BiYWO6, G/BiYWO3 and BiYWO6/Ce:CdS. In this scenario, ascorbic acid (AA) was exploited as an efficient and non-poisonous electron donor for scavenging photogenerated holes. The doping of Ce in CdS promoted its visible light absorption range and facilitated the charge transfer rate as well as hindered the h+/e- recombination. Moreover, the combination of G further promoted the electron carrier separation and transfer process due to its excellent electron collection and shuttling characteristic. Thus, the G/BiYWO6/Ce:CdS heterostructure was successfully served as a matrix for the PEC detection of tetracycline (Tc) at 0 V (vs Hg/Hg2Cl2). Under optimal conditions, the PEC aptasensor could offer a sensitive and specific detection limit (3 S/N) of Tc down to 0.01 ng/mL, as well as acceptable reproducibility, selectivity and storage stability, which opened up a promising pathway for the development of PEC biosensors.

Label-free Photoelectrochemical Aptasensor for the Determination of Carcinoembryonic Antigen Using a Cadmum Sulfide Quantum Dot Sensitized Titanium (IV) Oxide Nanotube Electrode

ABSTRACTA label-free photoelectrochemical aptasensor for the sensitive and selective determination of carcinoembryonic antigen was constructed based on a CdS quantum dot sensitized TiO2 nanotube electrode. TiO2 nanotubes with highly ordered structure and more active sites than bulk TiO2 were prepared with an electrochemical anodic oxidation process. The CdS quantum dots were immobilized on the TiO2 nanotubes using poly(diallyldimethylammonium chloride) as a bridge. Due to the energy level match between TiO2 and CdS, the CdS quantum dots/TiO2 nanotubes electrode exhibits excellent photoelectrochemical performance. The large surface area of the electrode also allows for capturing large numbers of aptamers. The fine photoelectrochemical performance and the large surface area of the electrode greatly enhanced the detection sensitivity. Under the optimal conditions, the prepared photoelectrochemical aptasensor presents desirable analytical properties for the determination of carcinoembryonic antigen in the range of 0.05 to 10 ng mL−1 with a detection limit of 0.014 ng mL−1. The application of the designed protocol was investigated by analyzing carcinoembryonic antigen in human serum samples with recoveries from 80.0 to 115.0%. This simple and sensitive method provides an alternative tool to standard biochemical assays.

A label-free photoelectrochemical aptasensor for bisphenol A based on surface plasmon resonance of gold nanoparticle-sensitized ZnO nanopencils

A simple and novel photoelectrochemical (PEC) aptasensor for selective detection of bisphenol A (BPA) was developed using surface plasmon resonance of Au nanoparticles activated ZnO nanopencils. With the irradiation of simulated light, the increased photocurrent of nano-Au/ZnO than that of pure ZnO nanopencil is induced by the hot electrons from excited Au nanoparticles. The perfect selectivity is attributed to the specific binding of BPA to its aptamer. With the addition of BPA, the conformation of aptamer changed to a G-quadruplex structure, which resulted in the blockages of photogenerated electron-transfer channels. Based on the above mechanisms and the optimized conditions, the assembled PEC aptasensor was linear with the concentration of BPA in the range of 1–1000nmolL−1 with a detection limit of 0.5nmolL−1. The presence of the same concentration and similar structure of other organics did not interfere in the detection of BPA and the recovery was between 96.2% and 108.4%. It has been successfully applied to the detection of BPA in drinking water and liquid milk samples. This PEC aptasensor has good performances in novelty, selectivity, sensitivity and low cost, and it provides an alternative approach to the detection of BPA.

A sensitive and label-free photoelectrochemical aptasensor using Co-doped ZnO diluted magnetic semiconductor nanoparticles.

Co-doped ZnO diluted magnetic semiconductor as a novel photoelectric beacon was first constructed for photoelectrochemical (PEC) aptasensor of acetamiprid. The fabricated PEC sensing is based on the specific binding of acetamiprid and its aptamer, which induces the decreasement of enhanced photocurrent produced by the electron donor of quercetin. Co(2+) doping has a beneficial effect in extending the band width of light absorption of ZnO into the visible region and to promote the separation of the photoinduced carriers due to the sp-d exchange interactions existing between the band electrons and the localized d electrons of Co(2+). The fabricated aptasensor was linear with the concentration of acetamiprid in the range of 0.5-800 nmolL(-1) with the detection limit of 0.18 nmolL(-1). The presence of same concentration of other conventional pesticides did not interfere in the detection of acetamiprid and the recovery is between 96.2% and 103.7%. This novel PEC aptasensor has good performances with high sensitivity, good selectivity, low cost and portable features. The strategy of Co-doped ZnO diluted magnetic semiconductor paves a new way to improve the performances of PEC aptasensor.

A label-free photoelectrochemical aptasensor based on nitrogen-doped graphene quantum dots for chloramphenicol determination.

A photoelectrochemical (PEC) sensing platform for chloramphenicol (CAP) detection was constructed using nitrogen-doped graphene quantum dots (N-GQDs) as transducer species and label-free aptamer as biological recognition element. N-GQDs, synthesized via a facile one-step hydrothermal method, were explored to achieve highly efficient photon-to-electricity conversion under visible light irradiation. The obtained N-GQDs were characterized by transmission electron microscopy (TEM), which displayed a narrow size distribution with a mean diameter of 2.14 nm. The X-ray photoelectron spectroscopic (XPS) and Fourier transform infrared spectroscopic (FT-IR) analysis confirmed that nitrogen was successfully doped in GQDs. The UV-visible absorption spectra indicated that nitrogen doping obviously enhanced the absorption of GQDs in visible light region. As a result, the PEC activity of GQDs was promoted by nitrogen doping. Additionally, the π-conjugated structure of N-GQDs provided an excellent platform for aptamer immobilization via π-π stacking interaction. Such an aptamer/N-GQDs based sensor showed a linear PEC response to CAP concentration in the range of 10-250 nM with a detection limit (3 S/N) of 3.1 nM. The developed PEC aptasensor exhibited high sensitivity and selectivity, good reproducibility and high stability.

Femtomole level photoelectrochemical aptasensing for mercury ions using quercetin–copper(II) complex as the DNA intercalator

An ultrasensitive and selective photoelectrochemical (PEC) aptasensor for mercury ions was first fabricated based on perylene-3, 4, 9, 10-tetracarboxylic acid/graphene oxide (PTCA/GO) heterojunction using quercetin–copper(II) complex intercalated into the poly(dT)–poly(dA) duplexes. Both the PTCA/GO heterojunction and the quercetin–copper(II) complex are in favor of the sensitivity for the fabricated PEC aptasensor due to band alignment and strong reduction capability, respectively. And they efficiently promote the separation of photoexcited carriers and enhance the photocurrent. The formation of thymine–Hg2+–thymine coordination chemistry resulted in the dehybridization of poly(dT)–poly(dA) duplexes and then the intercalator quercetin–copper(II) complex broke away from the surface of the PEC aptasensor. As the concentration of mercury ions increased, the photocurrent gradually decreased. The electrode response for mercury ions detection was in the linear range from 0.01pmolL−1 to 1.00pmolL−1 with the detection limit of 3.33fmolL−1. The label-free PEC aptasensor has excellent performances with ultrasensitivity and good selectivity besides the advantage of economic and facile fabrication. The strategy of quercetin–copper(II) complex as a novel DNA intercalator paves a new way to improve the performances for PEC sensors.

Phase diagram analysis using a partially associated solution model for III–V binary systems

An ultrasensitive and selective photoelectrochemical (PEC) aptasensor for mercury ions was first fabricated based on perylene-3, 4, 9, 10-tetracarboxylic acid/graphene oxide (PTCA/GO) heterojunction using quercetin–copper(II) complex intercalated into the poly(dT)–poly(dA) duplexes. Both the PTCA/GO heterojunction and the quercetin–copper(II) complex are in favor of the sensitivity for the fabricated PEC aptasensor due to band alignment and strong reduction capability, respectively. And they efficiently promote the separation of photoexcited carriers and enhance the photocurrent. The formation of thymine–Hg2+–thymine coordination chemistry resulted in the dehybridization of poly(dT)–poly(dA) duplexes and then the intercalator quercetin–copper(II) complex broke away from the surface of the PEC aptasensor. As the concentration of mercury ions increased, the photocurrent gradually decreased. The electrode response for mercury ions detection was in the linear range from 0.01 pmol L−1 to 1.00 pmol L−1 with the detection limit of 3.33 fmol L−1. The label-free PEC aptasensor has excellent performances with ultrasensitivity and good selectivity besides the advantage of economic and facile fabrication. The strategy of quercetin–copper(II) complex as a novel DNA intercalator paves a new way to improve the performances for PEC sensors.