New fluorescent labels for time-resolved detection of biomolecules

Diazaoxatriangulenium: synthesis of reactive derivatives and conjugation to bovine serum albumin

The azaoxa-triangulenium dyes are characterised by emission in the red and a long fluorescence lifetime (up to 25 ns). These properties have been widely explored for the azadioxatrianguelnium (ADOTA) dye. Here, the syntheses of reactive maleimide and NHS-ester forms of the diazaoxatriangulenium (DAOTA) system are reported. The DAOTA fluorophore was conjugated to bovine serum albumin (BSA) and investigated in comparison to the corresponding ADOTA-BSA conjugate. It was found that the fluorescence of DAOTA experienced a significantly higher degree of solvent quenching if compared to ADOTA as non-conjugated dyes in aqueous solution, while the fluorescence quenching observed upon conjugation to BSA was significantly reduced for DAOTA when compared to ADOTA. The differences in observed quenching for the conjugates can be explained by the different electronic structures of the dyes, which renders DAOTA significantly less prone to reductive photoinduced electron transfer (PET) quenching from e.g. tryptophan. We conclude that DAOTA, with emission in the red and inherent resistance to PET quenching, is an ideal platform for the development of long fluorescence lifetime probes for time-resolved imaging and fluorescence polarisation assay.

Multiplexed gold nanorod array biochip for multi-sample analysis

Optical transduction of biological bindings based on localized surface plasmon resonance (LSPR) of gold nanorods (GNRs) is attractive for label-free biosensing. The aspect ratio (AR) dependence of LSPR band maxima inherently provides an ideal multiplex mechanism. GNRs of selected sizes can be combined to ensure distinct plasmon peaks in absorption spectrum. Monitoring the spectral shift at the dedicated peaks allows for simultaneous detection of the specific analyte. Here, we first transformed the GNR's multiplexed biosensing capability to a robust chip-based format. Specifically, nanorods of AR 2.6 and 4.5 were assembled onto thiol-terminated substrates, followed by functionalization of respective antibodies to construct a GNR multiplex biochip. As a model system, concentrations of human IgG and rabbit IgG were simultaneously measured by correlating red-shifts at distinct resonance peaks caused by specific target binding. The calibration curves exhibited linear relationship between the spectral shift and analyte amount. The sensing performance in multi-analyte mode correlated nicely with those for single analyte detection with minimal cross-reactivity. Moreover, mixed GNRs can be deposited in controllable array pattern on the glass chip to analyze numerous samples at the same time. Each GNRs dot functioned independently as a multiplexed plamonic sensor. Coupled with microplate reader, this GNR nanoarray chip can potentially result in large scale assay of samples concurrently while for each sample, a multi-analyte detection simultaneously if desired. The concept shown in this work is simple and versatile that will definitely be a new paradigm in high-throughput protein biochip development in the era of nano-biosensing.

Fluorophore-mediated, fiber-optic, multi-analyte, immunosensing system for rapid diagnosis and prognosis of cardiovascular diseases

A prototype of a fiber-optic, multi-analyte, immunobiosensing system was developed to simultaneously quantify disease-representing biomarkers in blood plasma. This system was for simultaneous quantification of two different groups of multi-biomarkers related to cardiovascular diseases (CVD): anticoagulants (protein C, protein S, antithrombin III, and plasminogen) for deficiency diagnosis; and cardiac markers (B-type natriuretic peptide, cardiac troponin I, myoglobin, and C-reactive protein) for coronary heart disease diagnosis. As an initial effort towards the development of a disposable and easy-to-use sensing cartridge as a rapid diagnostic tool for CVD related diseases, a prototype of a flow control system was also developed to automatically perform simultaneous four-analyte quantification. Currently, the system is capable of quantifying the multiple anticoagulants in their clinically significant sensing ranges within 5 minutes, at an average signal-to-noise (S/N) ratio of 25. A simultaneous assay of the four cardiac markers can be performed within 10 min, at an average S/N ratio of 20. When this highly portable multi-analyte sensing system is completed and successfully tested for CVD patient's plasma, it can provide rapid (<10 min) and reliable diagnostic and prognostic information at a patient's bedside.

New fluorescent markers for the red region

Two new classes of fluorescent dyes have been developed as labels for the red region of the spectrum: amide-bridged benzopyrylium dyes and carbopyronin dyes. The fluorescence quantum yield ranges from 20 to 90%, the decay time from 1 to 4 ns. The pH- and solvent-dependence of absorption and fluorescence are described in detail. Covalent attachment is possible via activated carboxyl groups.

Capillary array scanner for time-resolved detection and identification of fluorescently labelled DNA fragments

The first capillary array scanner for time-resolved fluorescence detection in parallel capillary electrophoresis based on semiconductor technology is described. The system consists essentially of a confocal fluorescence microscope and a x,y-microscope scanning stage. Fluorescence of the labelled probe molecules was excited using a short-pulse diode laser emitting at 640 nm with a repetition rate of 50 MHz. Using a single filter system the fluorescence decays of different labels were detected by an avalanche photodiode in combination with a PC plug-in card for time-correlated single-photon counting (TCSPC). The time-resolved fluorescence signals were analyzed and identified by a maximum likelihood estimator (MLE). The x,y-microscope scanning stage allows for discontinuous, bidirectional scanning of up to 16 capillaries in an array, resulting in longer fluorescence collection times per capillary compared to scanners working in a continuous mode. Synchronization of the alignment and measurement process were developed to allow for data acquisition without overhead. Detection limits in the subzeptomol range for different dye molecules separated in parallel capillaries have been achieved. In addition, we report on parallel time-resolved detection and separation of more than 400 bases of single base extension DNA fragments in capillary array electrophoresis. Using only semiconductor technology the presented technique represents a low-cost alternative for high throughput DNA sequencing in parallel capillaries.

Sequence verification by hybridisation with fluorescent octanucleotides as a first step to a fluorescent sequencing by hybridisation protocol

Three sets of partly overlapping octanucleotides are 5' labelled with derivates of the fluorescence dyes fluorescein-, coumarine- and rhodamine, respectively. Hybridisation conditions are determined, under which all octanucleotides hybridise correctly against complementary target sequences bound on nylon membranes. Target sequences are three synthetic 48-mer oligonucleotides and herring sperm DNA, a positive control containing almost all possible octanucleotides. None of the octanucleotides hybridised to incorrect target sequences. Analysing these results, a given sequence could be unambiguously verified. A feature critical for the accuracy of the hybridisation is the temperature during the last washing step. This temperature can be estimated using the equation T = 19 - 0.4(G + C) + 0.15(G + C)2. Using octanucleotides labelled with three different colors, three hybridisations can be performed simultaneously.