Colorimetric aptamer based assay for the determination of fluoroquinolones by triggering the reduction-catalyzing activity of gold nanoparticles

The authors describe a colorimetric assay for the detection of fluoroquinolones (FQs). It is based on the use of gold nanoparticles (AuNPs) modified with complementary DNA strands and analyte-specific FQ-binding aptamers. The modified AuNPs possess enzyme-like activity that can catalyze the reduction of nitrophenol by NaBH₄. In the absence of ciprofloxacin, the flower-shape coating on the AuNPs prevents the reduction of yellow 4-nitrophenol. In the presence of ciprofloxacin, the DNA/aptamer flower leaves on the AuNPs and the AuNPs can exert their catalytic activity. This results in a color change from yellow to colorless. The assay is highly selective for FQs, fast (1 h), and has a limit of detection as low as 1.2 nM in case of ciprofloxacin. It was successfully applied to the determination of ciprofloxacin in spiked water, serum and milk samples to give LODs of 1.3, 2.6 and 3.2 nM, respectively.     

A Novel Electrochemical Method for the Sensitive Determination of Aflatoxin B1 Using a Bivalent Binding Aptamer-cDNA Structure

In this study, a simple electrochemical sensing platform with the employment of a bivalent binding aptamer-cDNA probe (BBA-cDNA) structure is constructed for the detection of aflatoxin B₁ (AFB₁) as a mycotoxin. The BBA-cDNA structure is composed of two strands of aptamer (Apts) and their complementary strand (CS). Using a simple but accurate design, the presented measurement approach showed enhanced sensitivity and selectivity for AFB₁ detection with a LOD of 0.1 ng/mL. The approach presented in this study can be applied to the development of biosensors for the measurement of various toxins by substituting the proper aptamers and complementary strands.     

Aptamer based fluorometric acetamiprid assay using three kinds of nanoparticles for powerful signal amplification

The authors describe an aptamer-based fluorometric assay for the insecticide acetamiprid. It is based on target-induced release of the fluorescein-labeled complementary strand of the aptamer (CS) from the aptamer/CS conjugate (dsDNA). Three kinds of nanoparticles with opposite effects on the fluorophore (FAM) were used. These include gold nanoparticles (AuNPs), single-walled carbon nanotubes (SWNTs) and silica nanoparticles (SiNPs) coated with streptavidin. In the presence of acetamiprid, FAM-labeled CS is released from the dsDNA-modified SNP-streptavidin complex and accumulates in the supernatant (phase I) after centrifugation. Fluorescence intensity decreases on addition of the supernatant to the SWNTs and AuNPs because they act as quenchers (phase II). In the absence of acetamiprid, the dsDNA-modified SiNP-streptavidin complex remains intact and no labeled CS is present in the supernatant containing the AuNPs and SWNTs. So, the relative fluorescence intensity is quite low. The assay is highly selective for acetamiprid and has a limit of detection (LOD) as low as 127 pM. The method was successfully applied to the determination of acetamiprid in spiked serum and water where it gave LODs of 198 and 130 pM, respectively.

Open image in new window

Graphical abstract In the absence of acetamiprid, the dsDNA-modified silica nanoparticle (SiNP)-streptavidin conjugate remains intact, leading to a very weak relative fluorescence intensity. In the presence of target, the dsDNA-modified SiNP-streptavidin complex is disassembled and FAM-labeled CS is released from the aptamer (Apt), resulting in a very strong relative fluorescence intensity.

     

New 12-tungstophosphate-based organic-inorganic hybrid. Synthesis, spectroscopic characterization, X-ray determination and thermal behavior

12-Tungstophosphate-based organic/inorganic hybrid, [HNMPA]₃[O₄₀PW₁₂].0.5NMPA.₂H₂O (NMPA = N-methylpropionamide) was synthesized and characterized by IR, UV-Vis, ¹H, ¹³C and ³¹P NMR spectroscopies, elemental analysis, TGA, DTA and single crystal X-ray determination. Full decomposition of the hybrid leads to WO₃ powder was studied by IR, SEM and XRD.