A new immunochemistry platform for a guideline-compliant cardiac troponin T assay at the point of care: proof of principle.

BACKGROUND: A multitude of troponin assays for the point-of-care (POC) have been developed showing a lack of analytical sensitivity and precision. We present a new platform solution for the high-sensitivity detection of cardiac troponin T (cTnT) in a 30 µL whole blood sample with a turnaround time of 11 min. METHODS: The immunoassay was completely run in a ready-to-use plastic disposable, a centrifugal microfluidic disc with fully integrated reagents. After the sample application, the assay was automatically processed by separating the cellular blood components via centrifugation, followed by incubation of a defined volume from the generated plasma with the immunoreagents. The fluorescence in the signal zone of a membrane was measured after its washing for the cTnT quantitation. RESULTS: A calibration curve, measured in whole blood samples spiked with native human cTnT, was generated covering a range up to a concentration of approximately 8300 ng/L. The lower detection limit was determined to be 3.0 ng/L. At a concentration of 14 ng/L, the 99th percentile value from the high-sensitivity cardiac troponin T (hs-cTnT) assay in the Elecsys® system, the imprecision (CV) was 3.8%. A CV profile indicated that the functional sensitivity for a CV <10% was 6.8 ng/L. The assay did not show any significant cross-reaction with human skeletal troponin T. We observed an excellent correlation with the hs-TnT Elecsys® assay for 49 clinical plasma samples (r=0.9744). CONCLUSIONS: The described technology shows that an analytical performance for a highly sensitive determination of cTnT can be achieved in a POC setting.

Long-range fluorescence quenching by gold nanoparticles in a sandwich immunoassay for cardiac troponin T.

We report the first homogeneous sandwich immunoassay with gold nanoparticles (AuNPs) as fluorescence quenchers. The sandwich assay is designed for the detection of the protein cardiac troponin T (cTnT) by its simultaneous interaction with two different antibodies, one attached to AuNPs and the other labeled with fluorescent dyes. We demonstrate the working principle of the assay and using time-resolved fluorescence spectroscopy, we determine the quenching efficiency of the gold nanoparticles. In spite of the relatively large separation distance between dye molecules and AuNPs, ranging from 3 to 22 nm, the AuNPs quench the fluorescence with efficiencies as high as 95%. A limit of detection of 0.02 nM (0.7 ng/mL) was obtained for cTnT, which is the lowest value reported for a homogeneous sandwich assay for cTnT. These results illustrate the use of metallic nanoparticles as fluorescence quenchers in immunoassays where the large biomolecules involved impose distances for which energy transfer between fluorophores would be inefficient.

Competitive homogeneous digoxigenin immunoassay based on fluorescence quenching by gold nanoparticles.

We report on a competitive, homogeneous immunoassay for the detection of the hapten digoxigenin. The assay is based on competitive fluorescence quenching by gold nanoparticles. Digoxigenin is indirectly labeled with the fluorophore Cy3B through bovine serum albumin and used as a marker. Gold nanoparticles functionalized with anti-digoxigenin antibodies serve as fluorescence quenchers. Free digoxigenin molecules in the analyte solution compete with the labeled markers for antibodies on the gold nanoparticles. The fluorescence signal depends linearly on the free digoxigenin concentration within a range of concentration from 0.5 to 3 ng mL(-1). The limit of detection is estimated as 0.2 ng mL(-1) and the limit of quantitation is estimated as 0.6 ng mL(-1). The method can be used to detect digoxin, a drug used to cure cardiac arrhythmia.

Gold nanostoves for microsecond DNA melting analysis.

In traditional DNA melting assays, the temperature of the DNA-containing solution is slowly ramped up. In contrast, we use 300 ns laser pulses to rapidly heat DNA bound gold nanoparticle aggregates. We show that double-stranded DNA melts on a microsecond time scale that leads to a disintegration of the gold nanoparticle aggregates on a millisecond time scale. A perfectly matching and a point-mutated DNA sequence can be clearly distinguished in less than one millisecond even in a 1:1 mixture of both targets.