Smartphone-based label-free photoelectrochemical sensing of cysteine with cadmium ion chelation

Anti-aggregation colorimetric sensing of cysteine using silver nanoparticles in the presence of Pb2

Using silver nitrate as the silver source and sodium borohydride as the reducing agent, we synthesized negatively charged silver nanoparticles (AgNPs). Subsequently, the AgNPs solution was mixed with positively charged lead ions, resulting in AgNPs aggregation via electrostatic interactions. This led to a color change in the solution from yellow to purple and eventually to blue-green. Our study focused on a colorimetric method that exhibited high selectivity and sensitivity in detecting cysteine using AgNPs-Pb2+ as a sensing probe. Upon the introduction of cysteine to the AgNPs-Pb2+ system, the absorbance of AgNPs increased at 396 nm and decreased at 520 nm. The formation of a complex between cysteine and lead ions prevented the aggregation of silver nanoparticles, enabling the colorimetric detection of cysteine. The relationship between the concentration of ΔA396/A520 and cysteine showed linearity within the range of 0.01 to 0.1 μM; the regression equation of the calibration curve is ΔA396/A520 = 9.0005c - 0.0557 (c: μM), with an R2 value of 0.9997. The detection limit was found to be 3.8 nM (S/N = 3). This method demonstrated exceptional selectivity and sensitivity for cysteine and was effectively used for the determination of cysteine in urine. Our findings offer a new perspective for the future advancement of anti-aggregation silver nanocolorimetry.

A Photoelectrochemical Sensor for the Sensitive Detection of Cysteine Based on Cadmium Sulfide/Tungsten Disulfide Nanocomposites

In this work, a CdS-nanoparticle-decorated WS2 nanosheet heterojunction was successfully prepared and first used to modify ITO electrodes for the construction of a novel photoelectrochemical sensor (CdS/WS2/ITO). The thin-film electrode was fabricated by combining electrophoretic deposition with successive ion layer adsorption and reaction techniques. The results indicated that the synthesized heterojunction nanomaterials displayed excellent photoelectrochemical performance which was much better than that of pristine CdS nanoparticles and 2D WS2 nanosheets. Owing to the formation of the surface heterojunction and the effective interfacial electric field, the enhanced separation of photogenerated electron-hole pairs led to a remarkable improvement in the photoelectrochemical activity of CdS/WS2/ITO. This heterojunction architecture can protect CdS against photocorrosion, resulting in a stable photocurrent. Based on the specific recognition between cysteine and CdS/WS2/ITO, through the specificity of Cd-S bonds, a visible-light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine, with an extremely low detection limit of 5.29 nM and excellent selectivity. Hence, CdS-WS2 heterostructure nanocomposites are promising candidates as novel advanced photosensitive materials in the field of photoelectrochemical biosensing.

Surface Plasmon Resonance Enhanced Photoelectrochemical Sensing of Cysteine Based on Au Nanoparticle-Decorated ZnO@graphene Quantum Dots

In this work, Au nanoparticle-decorated ZnO@graphene core-shell quantum dots (Au-ZnO@graphene QDs) were successfully prepared and firstly used to modify an ITO electrode for the construction of a novel photoelectrochemical biosensor (Au-ZnO@graphene QDs/ITO). Characterization of the prepared nanomaterials was conducted using transmission electron microscopy, steady-state fluorescence spectroscopy and the X-ray diffraction method. The results indicated that the synthesized ternary nanomaterials displayed excellent photoelectrochemical performance, which was much better than that of ZnO@graphene QDs and pristine ZnO quantum dots. The graphene and ZnO quantum dots formed an effective interfacial electric field, enhancing photogenerated electron-hole pairs separation and leading to a remarkable improvement in the photoelectrochemical performance of ZnO@graphene QDs. The strong surface plasmon resonance effect achieved by directly attaching Au nanoparticles to ZnO@graphene QDs led to a notable increase in the photocurrent response through electrochemical field effect amplification. Based on the specifical recognition between cysteine and Au-ZnO@graphene QDs/ITO through the specificity of Au-S bonds, a light-driven photoelectrochemical sensor was fabricated for cysteine detection. The novel photoelectrochemical biosensor exhibited outstanding analytical capabilities in detecting cysteine with an extremely low detection limit of 8.9 nM and excellent selectivity. Hence, the Au-ZnO@graphene QDs is a promising candidate as a novel advanced photosensitive material in the field of photoelectrochemical biosensing.

Dual-Signal Mode Ratiometric Photoelectrochemical Sensor Based on G-Quadruplex Hole Transport for Rapid and Sensitive Detection of miRNA-210

For rapid and sensitive detection of miRNA-210, which is important for improving the reliability of clinical diagnosis of breast cancer, a dual-signal mode ratiometric photoelectrochemical (PEC) sensor based on a Au/GaN photoanode is proposed. First, a DNA probe was designed that could complement the target miRNA-210. Then, another G-rich DNA sequence was designed to mismatch the probe and form a double-stranded DNA (dsDNA). Upon addition of the target, the dsDNA unwinds from its binding site and releases G-rich single-stranded DNA. In the presence of Mg2+ and K+, this single-stranded DNA molecule spontaneously forms a G-quadruplex structure, facilitating the rapid transport of photogenerated holes, thereby increasing the photocurrent response of Au/GaN and enabling sensitive label-free detection of miRNA-210. By control of different pH values, a response signal was generated at pH 8, while a reference signal was produced at pH 5. The designed PEC system shows a high potential for the development of miRNA-210 detection. Ultimately, the response signal-to-reference signal ratio was used as the variable, and a broad linear span ranging from 10 fM to 1 nM (R2 = 0.993) has been exhibited, with a detection threshold of 3 fM (S/N = 3). The designed PEC platform shows potential for the development of other disease markers.

Microperoxidase-11 functionalized nanozyme with enhanced peroxidase-mimicking activities for visual detection of cysteine

Various nanomaterials with peroxidase activity (nanozyme) have been designed for bio catalysis and biosensing, however, most of them need further design and modification of probe molecules for the specific binding reaction with targets. This results in a decrease in catalysis activity and hinders them to be perfect alternatives to natural enzyme in biosensing. In this work, an enhanced nanozyme was synthesized by functionalizing natural microperoxidase-11 (MP-11) on a hybrid graphene oxide-gold (GO-Au) material. The designed nanozyme showed an enhanced catalysis activity and realized a robust and efficient colorimetric detection of cysteine based on specific binding reaction between active iron center from MP-11 and thiol in cysteine. The enhanced properties show promising applications of complex nanozyme and provides a great opportunity for developing efficient sensing systems.

ZnO/Cu2O heterojunction integrated fiber-optic biosensor for remote detection of cysteine

Indium tin oxide, semiconductor nanomaterial ZnO, and Cu₂O were first loaded on the surface of the optical fiber to form an optical fiber probe. Large-volume macroscopic spatial light is replaced by an optical fiber path, and remote light injection is implemented. Based on the optical fiber probe, a photoelectrochemical biosensor was constructed and remote detection of cysteine was realized. In this tiny device, the optical fiber probe not only acts as a working electrode to react with the analyte but also directs the light exactly where it is needed. Simultaneously, the electrochemical behavior of cysteine on the surface of the working electrode is dominated by diffusion-control, which provides strong support for quantitative detection. Then, under the bias potential of 0 V, the linear range of the fiber-optic-based cysteine biosensor was 0.01∼1 μM, the regression coefficient (R²) value was 0.9943. In spiked synthetic urine, the detection of cysteine was also realized by the integrated biosensor. Moreover, benefiting from the low optical fiber loss, the new structure also possesses a unique remote detection function. This work confirms that photoelectrochemical biosensors can be integrated via optical fibers and retain comparable sensing performance. Based on this property, different materials can also be loaded on the surface of the optical fiber for remote detection of other analytes. It is expected to facilitate the research on fiber-optic-based integrated biosensors and show application prospects in diverse fields such as biochemical analysis and disease diagnosis.

Nanoengineering and green chemistry-oriented strategies toward nanocelluloses for protein sensing

As one of the most important functional organic macromolecules of life, proteins not only participate in the cell metabolism and gene regulation, they also earnestly protect the body's immunity system, leading to a powerful biological shield and homeostasis. Advances in nanomaterials are boosting the significant progress in various applications, including the sensing and examination of proteins in trace amount. Nanocellulose-oriented protein sensing is at the forefront of this revolution. The inherent feature of high biocompatibility, low cytotoxicity, high specific area, good durability and marketability endow nanocellulose with great superiority in protein sensing. Here, we highlight the recent progress of protein sensing using nanocellulose as the biosensor in trace amount. Besides, various kinds of construction strategies for nanocelluloses-based biosensors are discussed in detail, to enhance the agility and accuracy of clinical/medical diagnostics. Finally, several challenges in the approbatory identification of new approaches for the marketization of biomedical sensing that need further expedition in the future are highlighted.