Oligosaccharide-Assisted Direct Immunosensing of Small Molecules

A new approach for quantitative analysis of L-phenylalanine using a novel semi-sandwich immunometric assay

Here, we describe a novel method for L-phenylalanine analysis using a sandwich-type immunometric assay approach for use as a new method for amino acid analysis. To overcome difficulties of the preparation of high-affinity and selectivity monoclonal antibodies against L-phenylalanine and the inability to use sandwich-type immunometric assays due to their small molecular weight, three procedures were examined. First, amino groups of L-phenylalanine were modified by "N-Fmoc-L-cysteine" (FC) residues and the derivative (FC-Phe) was used as a hapten. Immunization of mice with bovine serum albumin/FC-Phe conjugate successfully yielded specific monoclonal anti-FC-Phe antibodies. Second, a new derivatization reagent, "biotin linker conjugate of FC-Phe N-succinimidyl ester" (FC(Biotin)-NHS), was synthesized to convert L-phenylalanine to FC-(Biotin)-Phe as a hapten structure. The biotin moiety linked to the thiol group of cysteine formed a second binding site for streptavidin/horseradish peroxidase (HRP) conjugates for optical detection. Third, a new semi-sandwich-type immunometric assay was established using pre-derivatized L-phenylalanine, the monoclonal anti-FC-Phe antibody, and streptavidin/HRP conjugate (without second antibody). Using the new "semi-sandwich" immunometric assay system, a detection limit of 35 nM (60 amol per analysis) and a detection range of 0.1-20 μM were attained using a standard L-phenylalanine solution. Rat plasma samples were analyzed to test reliability. Intra-day assay precision was within 6% of the coefficient of variation; inter-day variation was 0.1%. The recovery rates were from 92.4 to 123.7%. This is the first report of the quantitative determination of L-phenylalanine using a reliable semi-sandwich immunometric assay approach and will be applicable to the quantitative determination of other amino acids.

Attomolar determination of coumaphos by electrochemical displacement immunoassay coupled with oligonucleotide sensing

Coumaphos, an organophosphorus pesticide (OP) used worldwide, has raised serious public concerns due to its positive association with major types of cancer. Herein, a novel method for attomolar coumaphos detection was developed on the basis of an electrochemical displacement immunoassay coupled with oligonucleotide sensing. An optimized displacement immunoassay was constructed to improve the binding efficiency of an antigen-antibody pair, and a guanine-rich single-strand DNA label, in combination with oligonucleotide sensing, was used to amplify the detection signal with "direct" relationship to the analyte. As a result, coumaphos was sensitively determined from the enhanced catalytic cycle of guanine-Ru(bpy)(3)(2+) by chronoamperometry. The limit of detection (LOD) was down to 0.18 ng L(-1) (S/N = 3), which is equal to 49.6 amol in a sample solution of 100 μL. In comparison with conventional methods, the proposed method has the lowest LOD and better accessibility to high-throughput sensing systems. Besides, it can complete the whole analysis process in under 50 min and exhibits good performance of excellent selectivity to the OPs. With regard to the advantages of rapidity, convenience, low cost, and ease of operation, the proposed method has provided a promising platform capable of fast and in-field OP detection, which may make the system promising for potential applications in the detection of other small molecules.

A one-step sensitive dynamic light scattering method for detection using split aptamer fragments

A one-step sensitive method using dynamic light scattering (DLS) was introduced for direct detection of adenosine with high selectivity. For the first time, DLS was used to detect small molecules directly and quantitatively.