Highly Sensitive Immunoassay for the Diagnosis of Acute Myocardial Infarction Using Silica Spheres Encapsulating a Quantum Dot Layer

Abstract

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.

Quantum dot-layer-encapsulated and phenyl-functionalized silica spheres for highly luminous, colour rendering, and stable white light-emitting diodes

“…The absorption and PL spectra in Fig. 1e and f exhibit the same trends as those 12,13 previously reported for SQS. Both the absorption and PL intensities of SQ and SQS increased moderately to dramatically compared with those of the original QDs in the order QD < SQ < SQS.…”

“…For a red-emitting SQS Ph with highly enhanced PL, roughly 100 nm-sized SQS particles with emission peaks at 611 nm and 620 nm were prepared following a previously described method, 13 and their surface was functionalized via a sol-gel reaction of trimethoxy(2-phenylethyl)silane (TMPES) according to Scheme 1. Briefly, ligand-exchanged QDs with mercaptopropionic acid (Qs) were self-assembled on an aminopropyl-functionalized silica sphere (S) using electrostatic interaction, yielding an SQ solution.…”

“…SQS particles were synthesized by following a previously described method. 13 Briefly, the purchased silica particle solution (20 mL) was centrifuged after addition of 20 mL of ethanol and the solid was dispersed in 40 mL of methanol. After adding APTMS (∼5% of silica), the solution was refluxed overnight for amine-functionalization.…”

“…By reducing the aggregation between SQS spheres, roughly 100 nm-sized SQS spheres were improved to exhibit approximately 5-fold enhanced PL based on their ligand-exchanged QDs and 4-fold enhanced PL based on their original QDs. 13 However, the mechanism for PL enhancement is not yet known.…”

Surface modification of parylene-N with UV-treatment to enhance the protein immobilization

“…Parylenes with chemical functional groups, such as amino (ANH 2 ) [1][2][3][4], ethynyl (ACCH) [5,6], and formyl (ACHO) groups [7][8][9][10][11][12][13][14][15], have been particularly popular for covalently bonding to small proteins and peptides, which can be rinsed out during immunoassay processes [16]. Such parylenes with chemical functional groups have been produced through thermal deposition processes between the parylene precursors and the corresponding chemical functional groups [17].…”