Eight-channel SiNx microring-resonator based photonic biosensor for label-free fluid analysis in the optical C-band.

A lab-on-a-chip multichannel sensing platform for biomedical analysis based on optical silicon nitride (SiNx) microring-resonators (MRR) was established. The resonators were surface functionalized and finally combined with a microfluidic chamber for validation using an avidin-biotin ligand-binding assay. The results with a limit of detection (LOD) of 2.3∙10-5 and a mean intra-assay coefficient of variation (CV) of ±10.0 %, also under consideration of FDA guidelines, show promising future applicability for a wide variety of targets in the field of outpatient medical diagnostics and life science.Clinical Relevance- Biomarkers play a crucial role in physiological processes of the human body. To enable instantaneous and decentralized analysis of these markers, systems are needed that can be used in a laboratory-independent environment with minimal amounts of biofluid. An example is the utilization of such systems for neonates or infants.

Amplification by nucleic acid-templated reactions.

Nucleic acid-templated reactions enable the design of conditional reaction systems, in which bond formation occurs only when a particular DNA or RNA molecule is present. Such reaction systems are currently being explored for applications in DNA/RNA diagnosis, drug screening and as a means to design gene expression specific therapy. However, biological nucleic acid templates usually have low abundance. Therefore, either the targeted nucleic acid template has to be multiplied by means of an amplification step or the template itself has to act as a catalyst which amplifies product formation. This critical review highlights the recent advancements in nucleic acid-templated reactions that proceed with turnover in template and thereby provide a means of amplification. Improvements in reaction engineering and the development of new chemistries have pushed the limits from 10(1) to 10(2)-10(3) turnovers. This includes reaction systems that lead to the ligation of oligonucleotides or to the interconversion of appended functional groups beyond ligation as well as templated chemistries that enable the activation of catalysts for subsequent triggering of reactions between non-nucleotidic substrates. The present limitations and future opportunities are discussed.

DNA-triggered dye transfer on a quantum dot.

Nucleic acid-templated reactions are frequently explored tools in nucleic acid diagnosis. To enable a separation-free DNA detection, the reactive probe molecules require conjugation with reporter groups that provide measurable changes of an observable parameter upon reaction. A widely used, generic read-out method is based on fluorescence resonance energy transfer (FRET) between two appended dyes. Yet, spectral cross-talk usually limits the achievable enhancements of the FRET signal in DNA-directed chemistries. We describe a DNA-triggered transfer reaction which provides for strong increases of a fluorescent signal caused by FRET. The method may involve DNA- and PNA-based probes and is based upon a proximity-triggered transfer reaction which leads to the covalent fixation of a fluorescence dye on the surface of a quantum dot (QD). The transfer reaction brings the dye closer to the QD than hybridization alone. The resulting FRET signal is a specific monitor of the reaction and allows efficient discrimination of single base mismatched templates. Of note, the 35-fold increase of the FRET signal is measured at 310 nm apparent Stokes shift and turnover in template provides a means for signal amplification.

Promoting strand exchange in a DNA-templated transfer reaction.

Most DNA-templated reactions suffer from product inhibition. We explored a DNA-triggered fluorophor transfer reaction and demonstrated that comb-type polylysine-polydextran copolymers increase the turnover in template by promoting strand exchange.