A bead-based fluorescence immunosensing technique enabled by the integration of Förster resonance energy transfer and optoelectrokinetic concentration

Bead-based immunosensing has been growing as a promising technology in the point-of-care diagnostics due to great flexibility. For dilute samples, functionalized particles can be used to collect dispersed analytes and act as carriers for particle manipulation. To realize rapid and visual immunosensing, Förster resonance energy transfer (FRET) was used herein to ensure only the diabetic biomarker, lipocalin 1, to be detected. The measurement was made in an aqueous droplet sandwiched between two parallel plate electrodes. With an electric field and a focused laser beam applying on the microchip simultaneously, the immunocomplexes in the droplet were further concentrated to enhance the FRET fluorescent signal. The optoelectrokinetic technique, termed rapid electrokinetic patterning (REP), has been proven to be excellent in dynamic and programmable particle manipulation. Therefore, the detection can be complete within several tens of seconds. The lower detection limit of the REP-enabled bead-based diagnosis reached nearly 5 nM. The combinative use of FRET and the optoelectrokinetic technique for the bead-based immunosensing enables a rapid measure to diagnose early stage diseases and dilute analytes.

Colloidal nanomaterial-based immunoassay

Nanomaterials have been widely developed for their use in nanomedicine, especially for immunoassay-based diagnosis. In this review we focus on the use of nanomaterials as a nanoplatform for colloidal immunoassays. While conventional heterogeneous immunoassays suffer from mass transfer limitations and consequently long assay time, colloidal immunosupports allow target capture in the entire volume, thus speeding up reaction kinetics and shortening assay time. Owing to their wide range of chemical and physical properties, nanomaterials are an interesting candidate for immunoassay development. The most popular colloidal nanomaterials for colloidal immunoassays will be discussed, as well as their influence on immune reactions. Recent advances in nanomaterial applications for different formats of immunoassays will be reported, such as nanomaterial-based indirect immunoassays, optical-based agglutination immunoassays, resonance energy transfer-based immunoassays and magnetic relaxation-based immunoassays. Finally, the future of using nanomaterials for homogeneous immunoassays dedicated to clinical diagnosis will be discussed.

[Recent development of microfluidic diagnostic technologies]

Microfluidic devices exhibit a great promising development in clinical diagnosis and disease screening due to their advantages of precise controlling of fluid flow, requirement of miniamount sample, rapid reaction speed and convenient integration. In this paper, the improvements of microfluidic diagnostic technologies in recent years are reviewed. The applications and developments of on-chip disease marker detection, microfluidic cell selection and cell drug metabolism, and diagnostic micro-devices are discussed.

Lab-on-a-chip based immunosensor principles and technologies for the detection of cardiac biomarkers: a review

This review examines the current state of the art lab-on-a-chip and microfluidic based biosensor technologies used in the detection of cardiac biomarkers. The determination and quantification of blood based, cardiac biomarkers are crucial in the triage and management of a range of cardiac related conditions, where time delay has a major impact on short and longer-term outcomes of a patient. The design and manufacturing of biomarker detection systems are multi-disciplinary in nature and require researchers to have knowledge of both life sciences and engineering for the full potential of this field to be realised. This review will therefore provide a comprehensive overview of chip based immunosensing technology as applied to cardiac biomarker detection, while discussing the potential suitability and limitations of each configuration for incorporation within a clinical diagnostics device suitable for point-of-care applications.

On-chip aptamer-based sandwich assay for thrombin detection employing magnetic beads and quantum dots

In this paper, we report the development of an on-chip aptamer-based fluorescence assay for protein detection and quantification based on sandwich ELISA principles. Thrombin was selected as a model analyte to validate the assay design, which involves two DNA thrombin aptamers recognizing two different epitopes of the protein. Aptamer-functionalized magnetic beads were utilized to capture the target analyte, while a second aptamer, functionalized with quantum dots, was employed for on-chip detection. The binding of thrombin to the two aptamers via sandwich assay was monitored by fluorescence microscopy. The sandwich assay was performed on disposable microfluidic devices, fabricated on double-sided tapes and polymeric materials using a laser cutting approach. The approach enabled rapid thrombin detection with high specificity. Experimental conditions, such as reagent consumption and incubation time, were optimized in the microchip platform for the lowest limit of detection, highest specificity, and shortest assay time. The analytical performance of the microchip based assay was compared to that in the well plate format (generally utilized for ELISA-based methodologies). The results show that microfluidic chip proved to be a rapid and efficient system for aptamer-based thrombin assays, requiring only minimal (microliter) reagent use. This work demonstrated the successful application of on-chip aptamer-based sandwich assays for detection of target proteins of biomedical importance.

FRET for lab-on-a-chip devices - current trends and future prospects

This review focuses on the use of Förster Resonance Energy Transfer (FRET) to monitor intra- and intermolecular reactions occurring in microfluidic reactors. Microfluidic devices have recently been used for performing highly efficient and miniaturised biological assays for the analysis of biological entities such as cells, proteins and nucleic acids. Microfluidic assays are characterised by nanolitre to femtolitre reaction volumes, which necessitates the adoption of a sensitive optical detection scheme. FRET serves as a strong 'spectroscopic ruler' for elucidating the tertiary structure of biomolecules, as the efficiency of the non-radiative energy transfer is extremely sensitive to nanoscale changes in the separation between donor and acceptor markers attached to the biomolecule of interest. In this review, we will review the implementation of various microfluidic assays which employ FRET for diverse applications in the biomedical field, along with the advantages and disadvantages of the various approaches. The future prospects for development of microfluidic devices incorporating FRET detection will be discussed.

Immunoassays in microfluidic systems

Immunoassays have greatly benefited from miniaturization in microfluidic systems. This review, which summarizes developments in microfluidics-based immunoassays since 2000, includes four sections, focusing on the configurations of immunoassays that have been implemented in microfluidics, the main fluid handling modalities that have been used for microfluidic immunoassays, multiplexed immunoassays in microfluidic platforms, and the emergence of label-free detection techniques. The field of microfluidic immunoassays is continuously improving and has great promise for the future.