Method for rapid conjugation of recombinant photoprotein aequorin with streptavidin and application as a universal detection reagent for binding assays

Development of direct competitive enzyme-linked aptamer assay for determination of dopamine in serum

A rapid and cost-effective screening method based on a competitive enzyme-linked aptamer assay (ELAA) for dopamine (DA) in serum has been optimized and validated. In this paper, we report advantageous sensitivity and specificity of aptamer assays as compared to the existing antibody based-immunoassays. The RNA aptamer (67 mer) was immobilized via site-directed immobilization with biotin both at the 3'-end on aptamer and at neutravidin plate. Various factors such as incubation temperature, divalent ion - Mg(2+) ion and treatment of serum solution were evaluated for the performance of ELAA. The aptamer was incubated for 1h at 4°C in the assay buffer containing 5 mM Mg(2+) ion, and serum was diluted (1:9, serum:assay buffer) and filtrated through a 3 kDa dialysis membrane to extract the proteins present in the serum. Assay was performed with 0.01 μg mL(-1) of aptamer and 1.205×10(-7)M DA-HRP conjugate using the optimized method. A dose-response curve was constructed, and the limit of detection and a dynamic range for the DA were determined as 1.0×10(-12)M and four orders (1.0×10(-7)M to 5.0×10(-11) M) of magnitude, respectively. The correlation diagram of the absorbance obtained both in buffer and in serum has shown a good agreement with the correlation coefficient (R(2)=0.9872): Abs. (in serum)=0.9612×Abs. (in buffer)-0.0556. The cross-reactivity evaluation demonstrated that norepinephrine showed some cross-reactivity (3.68%) whereas 3-methoxytyramine, epinephrine, homovanillic acid and 3,4-dihydroxyphenylacetic acid showed almost no cross-reactivity (<1%). Percent recoveries of DA in serum were quite satisfactory (∼95%). This paper describes usefulness of the aptamer assay in monitoring DA in human serum.

Genotyping of single nucleotide polymorphisms by primer extension reaction and a dual-analyte bio/chemiluminometric assay

Primer extension reaction (PEXT) is the most widely used approach to genotyping of single nucleotide polymorphisms (SNP). It is based on the high accuracy of nucleotide incorporation by the DNA polymerase. We propose a dual-analyte bio/chemiluminometric method for the simultaneous detection of the PEXT reaction products of the normal and mutant allele in a high sample-throughput format. PCR-amplified DNA fragments that span the SNP of interest are subjected to two PEXT reactions using normal and mutant primers in the presence of digoxigenin-dUTP and biotin-dUTP. Both primers contain a d(A)30 segment at the 5'-end but differ in the final nucleotide at the 3'-end. Under optimized conditions only the primer that is perfectly complementary with the interrogated DNA will be extended by DNA polymerase and lead to a digoxigenin- or biotin-labeled product. The products of the PEXT reactions are mixed, denatured, and captured in microtiter wells through hybridization with immobilized oligo(dT) strands. Detection is performed by adding a mixture of antidigoxigenin-alkaline phosphatase (ALP) conjugate and a streptavidin-aequorin conjugate. The flash-type bioluminescent reaction of aequorin is triggered by the addition of Ca2+. ALP is then measured by adding the appropriate chemiluminogenic substrate. The method was evaluated by genotyping two SNPs of the human mannose-binding lectin gene (MBL2) and one SNP of the cytochrome P450 gene CYP2D6. Patient genotypes showed 100% concordance with direct DNA sequencing data.