Fluorescent Probe for Ag+ Detection Using SYBR GREEN I and C-C Mismatch

Development of an aptasensor for dibutyl phthalate detection and the elucidation of assay inhibition factors

We developed a fluorescence aptasensor (hereafter 'SG-aptasensor') using SYBR Green I, a newly truncated 20-mer aptamer, and probe DNA to detect dibutyl phthalate (DBP). The detection range of DBP was 0.1-100 ng L-1 with 0.08 ng L-1 as the limit of detection. To adapt the assay to environmental samples in the near future, possible inhibition factors (experimental and environmental) have been tested and reported. The experimental inhibitors included the incubation time, temperature, pH, and ionic strength. Consequently, temperature (2-25 °C) and pH (7.0-9.0) ranges did not significantly inhibit the assay. The incubation time required for sufficient reaction was at least 4 h, and a relative humidity <20% may have induced fluorescence quenching. Tris-HCl-based incubation buffer with excess ionic strength (more than 0.2 M NaCl) demonstrated an abnormal increase in fluorescence. Environmental inhibitors including cations (Mg2+, Ca2+, and Cu2+) and humic acids were tested. The fluorescence signal was significantly reduced (∼99%) by 100 mM Cu2+ compared to that by 0 mM Cu2+. In contrast, the reduction in fluorescence signal was marginal (<15%) when Mg2+ or Ca2+ ions were present. Inhibition of the assay was observed (∼28%) in the presence of 100 mg L-1 humic acids.

Selection and application of highly specific Salmonella typhimurium aptamers against matrix interference

In practical applications, the structure and performance of aptamers can be influenced by the presence of sample matrices, which interferes with the specific binding between the aptamer and its target. In this work, to obtain aptamer chains resistant to matrix interference, four typical food matrices were introduced as negative selection targets and selection environments in the process of selecting aptamers for Salmonella typhimurium using the systematic evolution of ligands by exponential enrichment (SELEX) technology. As a result, some highly specific candidate aptamers for Salmonella typhimurium (BB-34, BB-37, ROU-8, ROU-9, ROU-14, ROU-24, DAN-3, NAI-12, and NAI-21) were successfully obtained. Based on the characterization results of secondary structure, affinity, and specificity of these candidate aptamers, ROU-24 selected in the pork matrix and BB-34 selected in the binding buffer were chosen to develop label-free fluorescence aptasensors for the sensitive and rapid detection of the Salmonella typhimurium and verify the performance against matrix interference. The ROU-24-based aptasensor demonstrated a larger linear range and better specificity compared to the BB-34-based aptasensor. Meanwhile, the recovery rate of the ROU-24-based aptasensor in real sample detection (ranging from 94.2% to 110.7%) was significantly higher than that of the BB-34-based aptasensor. These results illustrated that the negative selection of food matrices induced in SELEX could enhance specific binding between the aptamer and its target and the performance against matrix interference. Overall, the label-free fluorescence aptasensors were developed and successfully validated in different foodstuffs, demonstrating a theoretical and practical basis for the study of aptamers against matrix interference.

Application of Pt@ZIF-8 nanocomposite-based electrochemical biosensor for sensitive diagnosis of tau protein in Alzheimer's disease patients

Alzheimer's disease (AD) is a progressive brain disorder characterized by the ongoing decline of brain functions. Studies have revealed the detrimental effects of hyperphosphorylated tau (p-tau) protein fibrils in AD pathogenesis, highlighting the importance of this factor in the early-stage detection of AD conditions. We designed an electrochemical immunosensor for quantitative detection of the cis conformation of the p-tau protein (cis-p-tau) employing platinum nanoparticles (Pt NPs) supported on zeolitic imidazolate frameworks (ZIF) for modifying the glassy carbon electrode (GCE) surface. Under optimum conditions, the immunosensor selectively and sensitively detected cis-p-tau within the broad linear range of 1 fg mL-1 to 10 ng mL-1 and the low limit of detection (LOD) of 1 fg mL-1 with desired reproducibility and stability. Furthermore, the fabricated immunosensor's performance was examined for the cis-p-tau analysis in the serum of AD patients, indicating its accuracy and feasibility for real-sample analysis. Notably, this is the first application of Pt@ZIF-8 nanocomposite in fabricating a valid immunosensor for selective cis-p-tau detection, even in the presence of trans-p-tau. It is worth mentioning that the enzyme-linked immunosorbent assay (ELISA) reference technique is not able to evaluate pico- or femtomolar concentrations of cis-p-tau, making the fabricated immunosensor superior for early-stage measurement and screening of AD.

A simple tag-free fluorometric aptasensing assay for sensitive detection of kanamycin

A novel label-free and enzyme-free fluorescence aptasensing assay that uses Sybr Green I (SGI) as the signal indicator for the kanamycin determination was designed. An aptamer-complementary strand (Apt/CP) conjugate was formed, which provided the intercalation sites for SGI and, therefore, a considerable fluorescent signal. The introduction of the target led to the separation of Apt from CP due to the high affinity of Apt toward kanamycin. Hence, the suitable intercalation gaps reduced, which resulted in a decrease in the generated fluorescent signal. Under optimized conditions, a broad linear concentration range from 0.05 μM to 20 μM and a limit of detection of 11.76 nM were obtained, confirming the ability of the fabricated aptasensor for sensitive and specific kanamycin detection in real samples such as milk and human serum. The aptasensing method has the potential to be extensively employed in the food industry and veterinary science due to its simplicity, sensitivity, user-friendly, and capability of on-site detection of kanamycin.

A Novel Minidumbbell DNA-Based Sensor for Silver Ion Detection

Silver ion (Ag⁺) is one of the most common heavy metal ions that cause environmental pollution and affect human health, and therefore, its detection is of great importance in the field of analytical chemistry. Here, we report an 8-nucleotide (nt) minidumbbell DNA-based sensor (M-DNA) for Ag⁺ detection. The minidumbbell contained a unique reverse wobble C·C mispair in the minor groove, which served as the binding site for Ag⁺. The M-DNA sensor could achieve a detection limit of 2.1 nM and sense Ag⁺ in real environmental samples with high accuracy. More importantly, the M-DNA sensor exhibited advantages of fast kinetics and easy operation owing to the usage of an ultrashort oligonucleotide. The minidumbbell represents a new and minimal non-B DNA structural motif for Ag⁺ sensing, allowing for the further development of on-site environmental Ag⁺ detection devices.

Felodipine Determination by a CdTe Quantum Dot-Based Fluorescent Probe

In this work, a CdTe quantum dot-based fluorescent probe was synthesized to determine felodipine (FEL). The synthesis conditions, structure, and interaction conditions with FEL of CdTe quantum dots were analysed by fluorescence spectrophotometry, Fourier transform infrared spectroscopy (FT-IR), X-ray diffraction (XRD), UV–visible spectroscopy, and TEM. The CdTe QD concentration was 2.0 × 10⁻⁴ mol/L. The amount of quantum dots controlled in the experiment was 0.8 mL. The controlled feeding ratio of N (Cd²⁺):N (Te²⁻):N (TGA) was 2:1:4, the heating temperature was 140 °C, the heating time was 60 min, and the pH of the QD precursor was adjusted to 11 for subsequent experiments. The UV–visible spectrum showed that the emission wavelength of CdTe quantum dots at 545 nm was the strongest and symmetric. The particle size of the synthesized quantum dots was approximately 5 nm. In the interaction of CdTe quantum dots with FEL, the FEL dosage was 1.0 mL, the optimal pH value of Tris-HCl buffer was 8.2, the amount of buffer was 1.5 mL, and the reaction time was 20 min. The standard curve of FEL was determined under the optimal synthesis conditions of CdTe quantum dots and reaction of CdTe quantum dots with FEL. The linear equation was Y = 3.9448x + 50.068, the correlation coefficient R2 was 0.9986, and the linear range was 5 × 10⁻⁶–1.1 × 10⁻⁴ mol/L. A CdTe quantum dot-based fluorescent probe was successfully constructed and could be used to determine the FEL tablet content.

Study on the mechanism of inhibiting patulin production by fengycin

Penicillium expansum is the main cause of apple rot. Besides, it can also produce mycotoxin patulin (PAT). Therefore, the search for substances that can inhibit the activity and toxigenicity of P. expansum has become a hot research topic. This study investigates the inhibitory effects of fengycin on patulin production in P. expansum. P. expansum was cultured under different environments with different concentrations of fengycin. The patulin content produced per unit weight of P. expansum mycelium was detected and determined by high pressure liquid chromatography (HPLC). Synergy brands (SYBR) GreenI Real-time PCR was used to detect the expression levels of 6-methylsalicylic acid synthase (6-MSAS) and isoepoxydon dehydrogenase (IDH), which were the key genes of producing patulin of P. expansum mycelium, in the conditions treated by fengycin and untreated. After fengycin treatments, not only the patulin content in every unit weight of P. expansum mycelium but also the expression level of 6-MSAS decreased significantly. The expression level of 6-MSAS of treatment was 0.11 folds of control. However, the expression level of IDH treated by fengycin decreased slightly. Fengycin could inhibit the P. expansum from producing patulin by downregulating the expression of key synthetic genes 6-MSAS.

A functional peptide-mediated colorimetric assay for mercury ion based on dual-modified gold nanoparticles

In the work, a rapid and accurate biosensor for mercury ions (Hg²⁺) was constructed, with which aggregation of dual-modified (DGPFHR- and CALNN-) gold nanoparticles (D/C-AuNPs) could be triggered by the high specificity of peptides to Hg²⁺. The given peptide DGPFHR possesses great capability of capturing Hg²⁺, accompanied by the conformational folding. Under the circumstances, D/C-AuNPs were employed as the detection probes to accomplish the quantitative analysis of Hg²⁺. This is primarily because the specific Hg²⁺-induced folding of peptides reduces the electrostatic repulsion and steric hindrance, thus accelerating the AuNPs aggregation. The principle and application potential of this proposal was proved by evidence. And the results demonstrated that Hg²⁺ ions could be selectively detected as low as 28 nM with a linear range of 100-800 nM. In consideration of superior simplicity, selectivity, accuracy and stability, the protocol was advantageous over other projects in practical measurement of various water samples.