Effect of perylene assembly shapes on photoelectrochemical properties and ultrasensitive biosensing behaviors toward dopamine.

In this study, a photoelectrochemical (PEC) sensor based on perylene diimide derivatives (PDIs) was developed for the ultrasensitive quantification of dopamine (DA). PDIs were able to form self-assembled semiconductor nanostructures by strong π-π stacking, suitable for photoactive substances. Moreover, the shape of the PDI significantly affected the PEC properties of these nanostructures. The results showed that amino PDI with two-dimensional (2D) wrinkled layered nanostructures exhibited superior PEC properties relative to one-dimensional (1D) nanorods and fiber-based nanostructures (methyl and carboxyl PDIs). Based on these results, a mechanism for PEC sensor action was then proposed. The presence of 2D amino-PDI resulted in accelerated charge separation and transport. Furthermore, dopamine acted as effective electron donor to cause an increase in photocurrent. The as-obtained sensor was then used to detect small molecules like DA. A blue light optimized sensor at an applied potential of 0.7 V showed a detection limit of 1.67 nM with a wide linear range of 5 nM to 10 µM. On the other hand, the sensor presented acceptable reliability in determining DA in real samples. A recovery rate between 97.99 and 101.0% was obtained. Overall, controlling the morphology of semiconductors can influence PEC performance, which is a useful finding for the future development of PEC sensors.

Amino-functionalized perylenediimide derivative with dual fluorescence emission for the detection of ascorbic acid in vivo and in vitro.

The rapid, sensitive, and selective detection of ascorbic acid (AA) is of significance in medical assays and diagnostics. In this work, a new aminoperylenediimide (APDI) derived ratiometric fluorescent probe based on the specific redox reaction of cobalt oxyhydroxide (CoOOH) and AA was constructed. APDI exhibited dual fluorescence emission peaks at 549 and 596 nm with an excitation wavelength of 494 nm. In the presence of CoOOH, the dual fluorescence could be quenched. The dominant fluorescence quenching mechanism was caused by the inner filter effect. Using the red emission as a reference, the fluorescence intensity ratio (F549 /F596 ) was linearly correlated with the concentration of AA over a range of 0.05 to 1 µM. The limit of detection for AA was found to be 17 nM. Importantly, the probe was successfully used to detect AA in living cells. Therefore, this high sensitivity and selectivity strategy could directly survey the AA levels in real samples.

Iodide/metal-organic frameworks (MOF) -mediated signal amplification strategy for the colorimetric detection of H2O2, Cr2O72- and H2S.

The analytical methods based on colorimetric detection of various analytes have attracted intensive interest. However, most of them display relatively low sensitivity. Herein, a novel colorimetric strategy based on iodide/metal-organic frameworks (MOF)-mediated amplification was developed for low-cost, naked-eye detection and quantification of H2O2,Cr2O72-, and H2S. Cu-MOFs could catalyze the oxidation of the colorless peroxidase substrate TMB to produce a blue product. The published researches mainly focused on the immobilization or integration of a macromolecule, such as natural enzymes, to enhance MOFs catalytic abilities. The use of small molecules to improve the catalytic performance of MOFs has rarely reported. Due to the negligible steric hindrance, iodide could easily be adsorbed in the framework pore of MOFs to conduct the synergic catalytic effect, and shows a high catalytic effect. As a result, the catalytic activity of Cu-MOFs was dramatically enhanced, and thus, the nanocatalyst could act as an amplifier system for target detection. The detection limits obtained by the amplified method are 25, 30, and 0.2 nM, respectively, which are about 200-fold lower than that of the unamplified colorimetric assays. The colorimetric strategy developed herein provides a novel system for the detection of low concentrations of analytes in complex biological samples.

Fe-MOFs as signal probes coupling with DNA tetrahedral nanostructures for construction of ratiometric electrochemical aptasensor.

A ratiometric electrochemical aptasensor is proposed for the detection of thrombin. In the sensor, the iron metal-organic frameworks (Fe MOFs)-labeled aptamer as signal tags was used as signal probe (SP), and the electrolyte solution [Fe(CN)6]3-/4- was utilized as an inner reference probe (IR). In the presence of thrombin, the signal of Fe-MOFs can be detected. Meanwhile, the signal of [Fe(CN)6]3-/4-IR almost remains stable. Accordingly, thrombin concentration can be monitored with the ratio response of IFe-MOFs-SP/I[Fe(CN)6]3-/4--IR. The proposed ratiometric biosensor owns a strong ability to eliminate the disturbance that arises from different DNA loading densities, environmental impact and instrumental efficiency. DNA nanotetrahedron (NTH) with three-dimensional (3D) scaffold can effectively eliminate nonspecific adsorption of DNA and protein. The accessibility of target molecules and loading amounts of signal substances could be increased because of the enhanced mechanical rigidity of well-designed 3D NTH. Thus, detection reproducibility and sensitivity can be further improved. Moreover, the biosensor only requires conjugation with one electroactive substance. The modification procedure can be greatly simplified. The biosensor owns high sensitivity with the detection limit of 59.6 fM. We expect that it will emerge as a generalized ratiometric sensor that may be useful for detecting target analytes.

Bifunctional MOFs-Based Ratiometric Electrochemical Sensor for Multiplex Heavy Metal Ions.

In this study, a ratiometric electrochemical sensor based on metal-organic frameworks (MOFs) was developed for sensing of multiplex metal ions. The bifunctional MOFs were prepared in a way to integrate two signal tags and a detection probe. In the presence of target metal ions, the target metal ions can replace the framework metal-ion center in the original MOFs through an ion-exchange reaction, leading to ratiometric electrochemical signals under different applied potentials. One consisted of the Cu2+ signal generated from electroactive MOFs selected as internal reference signals. The other consisted of the signal induced by other target metal ions. Using the Imetal ions/ICu2+ signal as the output, the prepared ratiometric probe was able to eliminate disturbance caused by the sensing environment. Moreover, the large surface area and abundant active sites in MOFs produced a multiplex ratiometric electrochemical sensor with improved characteristics in terms of reproducibility, stability, and sensitivity. The sensor was also simple without sophisticated instrumentation, amplification processes, or an acid dissolution/preconcentration procedure, hence promising for practical applications.

Development of Ochratoxin A Aptasensor Based on Au Nanoparticles@g-C3N4.

Ochratoxin is teratogenic, carcinogenic and immunotoxic to humans. It contains ochratoxin in many foods, so the detection of ochratoxin in food is particularly important. In this paper, gold nanoparticles (Au NPs)@g-C3N4 composite was synthesized by loading Au NPs on carbon nitride material, and it was immobilized on the surface of glassy carbon electrode by chitosan (Chit) as the substrate of electrochemical aptasensors. An ochratomycin A electrochemical aptasensor was constructed by hybridizing DNA1 and ochratoxin A (OTA) aptamers. The resulting hybrid strands were immobilized on the substrate of glassy carbon electrode. Electrochemical alternating current impedance (EIS) was used to detect the impedance value of the aptasensor when incubating different concentrations of OTA. The impedance value is inversely ratio to the concentration of OTA, achieving quantitative detection of OTA. The aptasensor can detect OTA with a linear range of 0.5-100 ng/mL, the linear correlation coefficient is 0.9506, and the detection limit is 0.167 ng/mL. This aptasensor provides a novel and efficient method for detecting OTA.

2D-porphrinic covalent organic framework-based aptasensor with enhanced photoelectrochemical response for the detection of C-reactive protein.

In this study, a novel photoelectrochemical (PEC) aptasensor based on two-dimensional (2D) porphyrinic covalent organic frameworks (p-COFs) for the label-free detection of C-reactive protein (CRP) is presented. The obtained p-COFs possess high conductivity and an improved stability due to strong and rigid covalent linkages. The introduction of p-COFs hinder the recombination of electrons and holes, decreasing their band gap (Eg), thereby which improved the photocurrent conversion efficiency. Compared with pure porphyrin, p-COFs exhibited enhanced photocurrent intensity. An amplified photocurrent conversion efficiency and enhanced photocurrent results from H2O2, which act as active molecules and electron donors. As an unprecedented application of COFs in PEC bioanalysis, the detection of CRP with a PEC aptasensor is presented. The assembly of a CRP aptamer on the surface of Ag nanoparticles hinders the electron transfer, resulting in the decrease of the photocurrent response. This PEC aptasensor exhibits good analytical performances such as a rapid response, high stability, wide linear range and excellent selectivity, making COFs promising candidates for PEC bioanalysis.