Commercial ELISA kits for
substance P (
SubP), which are helpful for the clinical diagnosis of acute
myocardial infarction, are limited in efficacy because of low sensitivity. A highly sensitive immunoassay was developed using
silica spheres encapsulating a
quantum dot-layer (SQS) and labeling
antibodies, on a
Parylene A-modified plate. The high sensitivity was possible by taking advantage of the enhanced photoluminescence of the SQS and dense immobilization of
SubP on a
Parylene A-modified plate.
Glutaraldehyde was used for cross-linking of SQS to the anti-
SubP antibody and
SubP to the
Parylene A coating. The SQS-linked
immunosorbent assay (SQSLISA) was optimized and validated. The dynamic range for the assay was 1-10000 pg/mL with a linear correlation factor of 0.9992 when the competitive SQSLISA was employed. The intra- and interday accuracies were 93-100% and 87-122%, respectively. The reproducibility was lower than 11%. The developed method was applied to clinical samples collected from healthy controls (
n = 30) and acute
myocardial infarction (n = 16) and it displayed a high correlation with the commercial ELISA kit, with a limit of detection that was 30-fold lower. Clinical sample analysis confirmed that
SubP is a promising diagnostic marker for acute
myocardial infarction. The SQSLISA is expected to be a practical and useful assay tool.