Photoelectrochemical and electrochemical ratiometric aptasensing: A case study of streptomycin

Scientific Insights into the Quantum Dots (QDs)-Based Electrochemical Sensors for State-of-the-Art Applications

Size-dependent optical and electronic properties are unique characteristics of quantum dots (QDs). A significant advantage is the quantum confinement effect that allows their precise tuning to achieve required characteristics and behavior for the targeted applications. Regarding the aforementioned factors, QDs-based sensors have exhibited dramatic potential for the diverse and advanced applications. For example, QDs-based devices have been potentially utilized for bioimaging, drug delivery, cancer therapy, and environmental remediation. In recent years, use of QDs-based electrochemical sensors have been further extended in other areas like gas sensing, metal ion detection, monitoring of organic pollutants, and detection of radioactive isotopes. Objective of this study is to rationalize the QDs-based electrochemical sensors for state-of-the-art applications. This review article comprehensively illustrates the importance of aforementioned devices along with sources from which QDs devices have been formulated and fabricated. Other distinct features of QDs devices are associated with their extremely high active surfaces, inherent ability of reproducibility, sensitivity, and selectivity for the targeted analyte detection. In this review, major categories of QD materials along with justification of their key roles in electrochemical devices have been demonstrated and discussed. All categories have been evaluated with special emphasis on the advantages and drawbacks/challenges associated with QD materials. However, in the interests of readers and researchers, recent improvements also have been included and discussed. On the evaluation, it has been concluded that despite significant challenges, QDs-based electrochemical sensors exhibit excellent performances for state-of-the-art and targeted applications.

A bulit-in self-calibration ratiometric self-powered photoelectrochemical sensor for high-precision and sensitive detection of microcystin-RR

A novel high-precision aptasensor of microcystin-RR (MC-RR) is developed based on a ratiometric self-powered photoelectrochemical platform. In detail, the defective MoS2/Ti3C2 nanocomposite with good photoelectric activity was designed to serve as the photoanode of the sensor for enhancing the signal and improving the detection sensitivity. In order to effectively eliminate external interferences, the key point of this ratiometric device is the introduction of the spatial-resolved technique, which includes the detection section and the reference section, generating reference signals and response signals, respectively. Moreover, output power was used as the detection signal, instead of the traditional photocurrent or photovoltage. Further, potassium persulfate was introduced as electron acceptor, which was beneficial for improving the electron transport efficiency, hindering electron-hole recombination, and significantly promoting the performance of the sensor. Finally, aptamer was adopted as recognition element to capture MC-RR molecules. The prepared sensor had a linear range from 10-12 to 10-6 M, and the detection limit was 5.6 × 10-13 M (S/N = 3). It has good precision, selectivity, and sensitivity, which shows great prospects in the on-site accurate analysis of samples with high energy output in the self-powered sensing field.

In-depth interpretation of aptamer-based sensing on electrode: Dual-mode electrochemical-photoelectrochemical sensor for the ratiometric detection of patulin

Electrochemical aptasensors have been extensively used to quantify food contaminants (e.g., mycotoxin) by using high-affinity aptamer for target recognition. Yet, analytical performance of aptasensors using different aptamers can be varied for the same target. Here, four aptamers with different sequences (i.e., A22, A34, A42, and A45) of patulin (PAT) were selected to estimate sensing behaviors at electrodes with electrochemical (EC) and photoelectrochemical (PEC) assays. Synergistic effect of steric hindrance and electron transfer distance was found to significantly affect EC and PEC response for PAT at aptasensors fabricated with A22, A34, A42, or A45. Eventually, A22 emerged to be the optimal aptamer for aptasensing, despite the highest affinity of A42 to PAT. The A22-based EC-PEC dual-mode ratiometric aptasensor offered a linear range of 50 fg mL^-1 - 500 ng mL^-1 with a detection limit of 30 fg mL^-1 for PAT, and it was applied to apple product (i.e., juice, puree) analysis.

Hairpin DNA-enabled ratiometric electrochemical aptasensor for detection of malathion

A hairpin DNA-enabled ratiometric electrochemical aptasensor is reported for sensitive and reliable detection of malathion (MAL). The approach employs hairpin DNA (ferrocene-labeled, Fc-hDNA) as a carrier to hybridize MAL aptamers (methylene blue-labeled, MB-Apt) to form double-stranded DNA structures on an electrode. The presence of MAL induces the removal of aptamers, and hDNA re-forms hairpin structures, causing a decrease in the oxidation current of MB (I_MB) and an increase in the oxidation current of Fc (I_Fc). The ratiometric signal of I_Fc/I_MB responds quantitatively to MAL concentrations. To compare analytical performances, a linear single-stranded DNA (ssDNA) is also used to construct the ssDNA-based aptasensor. We demonstrate that hairpin DNA possessing a rigid two-dimensional structure can improve the assembly efficiency of aptamers and the stability of redox probes. The approach combines the advantages of the ratiometric electrochemical method with hairpin DNA-based conformational switching probes, enabling hDNA-based aptasensor with enhanced sensitivity and reliability, offering a linear range of 0.001 to 1.0 ng mL^-1. The platform was applied to detect MAL in lettuce, and the statistical analysis indicated that no significant differences were found between the developed platform and HPLC-MS.

Nucleotide detection mechanism and comparison based on low-dimensional materials: A review

The recent pandemic has led to the fabrication of new nucleic acid sensors that can detect infinitesimal limits immediately and effectively. Therefore, various techniques have been demonstrated using low-dimensional materials that exhibit ultrahigh detection and accuracy. Numerous detection approaches have been reported, and new methods for impulse sensing are being explored. All ongoing research converges at one unique point, that is, an impetus: the enhanced limit of detection of sensors. There are several reviews on the detection of viruses and other proteins related to disease control point of care; however, to the best of our knowledge, none summarizes the various nucleotide sensors and describes their limits of detection and mechanisms. To understand the far-reaching impact of this discipline, we briefly discussed conventional and nanomaterial-based sensors, and then proposed the feature prospects of these devices. Two types of sensing mechanisms were further divided into their sub-branches: polymerase chain reaction and photospectrometric-based sensors. The nanomaterial-based sensor was further subdivided into optical and electrical sensors. The optical sensors included fluorescence (FL), surface plasmon resonance (SPR), colorimetric, and surface-enhanced Raman scattering (SERS), while electrical sensors included electrochemical luminescence (ECL), microfluidic chip, and field-effect transistor (FET). A synopsis of sensing materials, mechanisms, detection limits, and ranges has been provided. The sensing mechanism and materials used were discussed for each category in terms of length, collectively forming a fusing platform to highlight the ultrahigh detection technique of nucleotide sensors. We discussed potential trends in improving the fabrication of nucleotide nanosensors based on low-dimensional materials. In this area, particular aspects, including sensitivity, detection mechanism, stability, and challenges, were addressed. The optimization of the sensing performance and selection of the best sensor were concluded. Recent trends in the atomic-scale simulation of the development of Deoxyribonucleic acid (DNA) sensors using 2D materials were highlighted. A critical overview of the challenges and opportunities of deoxyribonucleic acid sensors was explored, and progress made in deoxyribonucleic acid detection over the past decade with a family of deoxyribonucleic acid sensors was described. Areas in which further research is needed were included in the future scope.

Bi/BiVO4/NiFe-LDH heterostructures with enhanced photoelectrochemical performance for streptomycin detection

Streptomycin (STR) plays an essential role in bacterial infection treatments. Selectivity and sensitivity of photoelectrochemical (PEC) sensors are the two most important parameters, which can be measured using the photosensitivity of its active material. We prepared a novel PEC sensor to detect STR using Bi/BiVO₄/LDH (layered double hydroxides) heterostructures as an active material, which is photoactive in the visible light wavelength range. The simultaneous presence of LDH and Bi/BiVO₄ enhanced the material photocurrent response, which was linear to the STR concentrations in the 0.01-500 nmol/L range. The STR detection limit by this sensor was 0.0042 nmol/L. Our novel PEC-based sensing strategy includes using an ultra-sensitive and highly selective sensor for STR detection. Additionally, the two-pot synthesis of Bi/BiVO₄/LDH developed in this work is environmentally friendly.

Cytochrome c/Multi-walled Carbon Nanotubes Modified Glassy Carbon Electrode for the Detection of Streptomycin in Pharmaceutical Samples

A novel electrochemical glassy carbon electrode modified with a multi-walled carbon nanotube, cytochrome c (Cyt c) and zinc oxide nanoparticles (ZnONPs) was fabricated to increase the sensitivity of electrode for the detection of streptomycin (STN) in certain pharmaceutical samples. Cyclic voltammetry (CV) and differential pulse voltammetry techniques were used for an electrochemical characterization of the electrode. Furthermore, the electrochemical biosensor construction phases were examined by using X-ray diffraction (XRD), transmission electron microscopy (TEM) and Fourier-transform infrared spectroscopy (FTIR). Under the optimal experimental conditions, the electrode offers a high selectivity and sensitivity signaling in the co-existence method of STN with the linear concentration ranging from 0.02 to 2.2 μM. The detection limits (LOD) and limit of quantification (LOQ) were found to be 0.0028 and 0.0562 μM, respectively. The fabricated sensing electrode has good stability, reproducibility and sensitivity towards STN in the pharmaceutical samples. Preliminary determinations of binding sites within the specified grid box size, which covers both Cyt c and STN, were done by molecular docking analysis. Moreover, density functional theory (DFT) computations were performed to provide insightful information into the optimized geometry of STN.

Selective and sensitive photoelectrochemical aptasensor for streptomycin detection based on Bi4VO8Br/Ti3C2 nanohybrids

Sensitive detection of streptomycin (STR) has attracted increasing attention worldwide because of the relationship between food security and human health. In this paper, Bi₄VO₈Br/Ti₃C₂ nanohybrids were obtained by one-pot solvent hydrothermal method. It was modified on ITO electrode, and STR aptamer was acted as the recognition element. With excellent photoelectrochemical (PEC) performance of Bi₄VO₈Br/Ti₃C₂ nanohybrids, an "on-off-on" PEC aptasensor for STR detection was effectively developed. Compared with pure Bi₄VO₈Br, the photocurrent intensity of as-prepared Bi₄VO₈Br/Ti₃C₂ nanohybrids was about 9 times higher, which ascribed to the highly conductive of Ti₃C₂, driving the photogenerated electrons transferred to the ITO electrode rapidly, so that the recombination of photogenerated electron and hole pairs was inhibited viably. Furthermore, the constructed "on-off-on" PEC aptasensor accomplished STR detection with high sensitivity, excellent specificity and distinguished repeatability in honey. The photocurrent increased with the increment of STR concentration with the linear range from1 nM to 1000 nM, and the detection limit of 0.3 nM (S/N = 3). Compared with the national standard method (SN/T 1925-2007), the as-constructed PEC sensor showed the consistent results.