ABSTRACT
This correspondence presents a new strategy for detecting biological molecules that relies on competitive exchange interactions of an analyte with two-component molecular tethers attaching superparamagnetic microspheres (4 microm in diameter) to a sensor surface. The individual tethers consist of an antibody-antigen complex and are designed to selectively detect antigenic proteins in a sensitive reagentless fashion. In order to impart a driving force to the otherwise free energy neutral antibody-antigen exchange equilibrium, a small mechanical force of approximately 10 pN was applied to stretch the antibody-antigen tethers using a massively parallel magnetic tweezers device. The experimental work was carried out with human cardiac troponin I. This serum heart attack marker was used as an example of analytes of credible relevance to biomedical diagnostics. The initial results illustrate the functioning of a cardiotroponin sensor and offer a preliminary estimate of its sensitivity of 16 pM.
Subject(s)
Biosensing Techniques/methods , Immunoassay/methods , Magnetics , Microspheres , Troponin I/analysis , Biosensing Techniques/instrumentation , Equipment Design , Humans , Immunoassay/instrumentation , Myocardium/chemistry , Sensitivity and Specificity , Troponin I/immunologyABSTRACT
BACKGROUND: This study determines the analytical characteristics of the i-STAT cardiac troponin I assay (cTnI; i-STAT, Princeton, NJ), a 10-min POC assay, designed to be performed at the bedside. METHODS: Three different hospitals participated in a patient specimen and analytical validation study (n=186) for the i-STAT cTnI assay carried out in real time. A total of 186 whole blood specimens (lithium heparin) were collected from patients presenting with symptoms suggestive of acute coronary syndromes (ACS) for correlation studies as well as from 162 healthy subjects for reference interval determination. Factors studied included antibody specificity, detection limit, imprecision, linearity, assay specificity, sample type stability, interferences, reference limit determination and comparison vs. the Dade Stratus CS cTnI assay. RESULTS: Total imprecision (CV) of 10% and 20% were seen at 0.09 and 0.07 microg/l, respectively. The detection limit was 0.02 microg/l. The 99th percentile reference limit was 0.08 microg/l. The assay was not affected by common interferents. An equimolar response within 5% was found for reduced and phosphorylated forms of TIC and IC complexes. Regression analysis for the i-STAT cTnI between whole blood and plasma specimens and for whole blood between the i-STAT and Stratus CS cTnI assays demonstrated slopes of 1.06 and 0.89, respectively. CONCLUSIONS: The i-STAT cTnI assay is a sensitive and precise monitor of cTnI, poised for point-of-care/near bedside clinical utilization for triage, diagnostics and risk management of acute coronary syndrome patients.
