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A new approach to perform electrochemical immunoassay based on the utilization of encapsulated microcrystal was developed. The microcrystal labels create a 'supernova effect' upon exposure to a desired releasing agent. The microcrystal cores dissolve, and large amounts of signal-generating molecules diffuse across the capsule wall into the outer environment. Layer-by-Layer (LbL) technology was employed for the encapsulation of electrochemical signal-generating microcrystals (ferrocene microcrystals). The encapsulated microcrystals were conjugated with antibody molecules through the adsorption process. The biofunctionalized microcrystals were utilized as a probe for immunoassays. The microcrystal-based label system provided a high-signal molecule to antibody (S/P) ratio of [10.sup.4]-[10.sup.5]. Microcrystal biolabels with different antibody surface coverage (1.60-5.05 mg [m.sup.-2]) were subjected to a solid-phase immunoassay for the detection of mouse immunoglobulin G (M-IgG) molecules. The microcrystal-based immunoassay for the detection of M-IgG performed with microcrystals having antibody surface coverage of 5.05 mg [m.sup.-2] showed a sensitivity of 3.93 nA [micro][g.sup.-1] [L.sup.-1] with a detection limit of 2.82 [micro]g [L.sup.-1].

Using heart-type fatty acid-binding protein (H-FABP) as an early cardiac marker for diagnosis of acute myocardial infarction (AMI) soon after the onset of symptoms requires a rapid assay. A one-step test called, CardioDetect®, is used for detection of H-FABP in whole blood sample. Thirty patients suspected of AMI presenting to the emergency department within 12 hours after onset were enrolled in this study. The diagnostic performance of CardioDetect® was compared with different cardiac markers. There were 59.1% of patients with positive H-FABP within 6 hours after onset, while there were only 18.2% with positive cardiac troponin I (cTnI). Results indicated the diagnostic power of H-FABP for AMI was significantly higher than that of cTnI. The sensitivity of H-FABP was 81.8%, which was higher than those of the other cardiac markers, while the specificity was comparable. The area under the receiver operating characteristic curve for H-FABP was 0.909, which was significantly larger than the others. With this rapid and sensitive immunotest, H-FABP could be soon introduced in clinical practice in combination with well-established markers like troponins. [ABSTRACT FROM AUTHOR]