Mercaptopropylsilatrane (MPS) was investigated as a novel self-assembled film on silica surfaces and also as a novel adhesive layer for the construction of a gold colloid monolayer on silica surfaces.

Surface modification of a polymer substrate with a mercapto functionality is crucial in many applications such as flexible circuitry and point-of-care biosensors. We present here a novel bifunctional molecular adhesive, 3-mercaptopropylsilatrane (MPS), as an interface between polymer and metal surfaces. Under ambient conditions, surface modification of polymer surfaces with a mercapto functionality can be achieved with low concentration (0.46 mM) of MPS in aqueous solvent (50% ethanol) in a short time (<30 min). Three popular polymers for optical sensors, polycarbonate, polyethylene terephthalate, and poly(methyl methacrylate), were employed as substrates, and MPS films formed on these substrates were examined and compared with that on a glass substrate. The films were characterized by UV-vis spectroscopy, water contact angle, X-ray photoelectron spectroscopy, and atomic force microscopy. MPS was also used as a bifunctional linker for the construction of a gold nanoparticle (AuNP) sub-monolayer on these polymer surfaces. Under optimized preparation conditions, the absorbance and full width at half-maximum of the plasmon band are comparable to those of a AuNP-modified glass substrate. Hence, MPS may have a potential to be a key component in polymer substrate-based localized surface plasmon resonance sensors. A self-catalytic surface reaction mechanism is also proposed to account for the results. As compared to a glass surface with a high number of silanol groups, the successful formation of an MPS film on polymer surfaces with relatively few reactive sites is probably due to the lateral polymerization of MPS starting from a condensed MPS molecule on a reactive site of a polymer surface.

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Mercury ion (Hg 2+ ) is extremely toxic even at very low concentrations and its detection mainly relies on bulky and high-cost analytical instruments. Here, we introduce a fast and ultrasensitive biosensing method developed by the integration of fiber optic particle plasmon resonance and a highly selective molecular beacon with a stem-loop DNA structure immobilized on the unclad surface of an optical fiber. In the presence of Hg 2+ ions and a free assisting DNA probe, the stem-loop opens and forms thymine−Hg 2+ −thymine complexes. A DNA reporting probe conjugated to gold nanoparticles is used as a label to interrogate the recognition event by binding with the terminal DNA binding domain of the opened stem-loop. The method provides a wide linear range of at least 5 orders from 10 −14 to 10 −9 M and an extremely low detection limit of 4.37 fM (0.876 ppq). It takes less than 15 min to analyze the concentration of Hg 2+ ions in aqueous samples. The method is desirable for point-of-use applications because of its low-cost instrumentation and sensor chips, easy operation, and portability.

The N-terminal pro-brain natriuretic peptide (NT-proBNP) is considered an important blood biomarker for heart failure. Herein, we report about a fiber optic nanogold-linked immunosorbent assay (FONLISA) method for the rapid, sensitive, and low-cost detection of NT-proBNP. The method is based on a sandwich immunoassay approach that uses two monoclonal NT-proBNP antibodies, a capture antibody (AbC), and a detection antibody (AbD). AbD is conjugated to a free gold nanoparticle (AuNP) to form the free AuNP@AbD conjugate, and AbC is immobilized on an unclad segment of an optical fiber. The detection of analyte (A), in this case NT-proBNP, is based on the signal change due to the formation of an AuNP@AbD–A–AbC complex on the fiber core surface, where a green light transmitted through the optical fiber will decrease in intensity due to light absorption by AuNPs via the localized surface plasmon resonance effect. This method provides a wide linear dynamic range of 0.50~5000 pg·mL−1 and a limit of detection of 0.058 pg·mL−1 for NT-proBNP. Finally, the method exhibits good correlation (r = 0.979) with the commercial central laboratory-based electrochemiluminescent immunoassay method that uses a Roche Cobas e411 instrument. Hence, our method is potentially a suitable tool for point-of-care testing.