A portable electrochemical immunosensor for highly sensitive point-of-care testing of genetically modified crops

The wide cultivation of genetically modified (GM) crops has raised concerns on the risks to humans and the environment. 5-enolpyruvylshikimate-3-phosphate synthase isolated from Agrobacterium species strain CP4 (CP4-EPSPS) protein is most widely present in these crops. Therefore the measurement of CP4-EPSPS sensitively in a point-of-care testing (POCT) manner for the screening of transgenic plants is demanded. To date the development of quantitative POCT system has not yet been reported. In presented study, an electrochemical immunosensor towards CP4-EPSPS has been fabricated by integrating a portable bioanalytical device with a disposable screen-printed carbon electrode (SPCE) for POCT of GM crops. The dual-functionalized AuNPs were used as nanoprobes and prepared by simultaneously tagging horseradish peroxidase (HRP) and antibody on AuNPs with an exceptionally simple protocol. The sensitivity of the developed nanoprobe-based immunosensor was 62.5-fold higher than that using HRP-labeled antibody. As a result, the proposed immunosensor using SPCE could detect CP4-EPSPS down to 0.050 ng mL^-1 with the linear range of 0.10-10 ng mL^-1 within 65 min. In addition, the developed method has been validated with genuine GM crops and the results show a good correlation coefficient of 0.9909 compared with those of a commercial ELISA kit. Therefore, this portable electrochemical immunosensor is suitable for rapid and sensitive detection and provides a convenient and reliable platform for POCT assay.

Label-free imaging of neurotransmitters in live brain tissue by multi-photon ultraviolet microscopy

Visualizing small biomolecules in living cells remains a difficult challenge. Neurotransmitters provide one of the most frustrating examples of this difficulty, as our understanding of signaling in the brain critically depends on our ability to follow the neurotransmitter traffic. Last two decades have seen considerable progress in probing some of the neurotransmitters, e.g. by using false neurotransmitter mimics, chemical labeling techniques, or direct fluorescence imaging. Direct imaging harnesses the weak UV fluorescence of monoamines, which are some of the most important neurotransmitters controlling mood, memory, appetite, and learning. Here we describe the progress in imaging of these molecules using the least toxic direct excitation route found so far, namely multi-photon (MP) imaging. MP imaging of serotonin, and more recently that of dopamine, has allowed researchers to determine the location of the vesicles, follow their intracellular dynamics, probe their content, and monitor their release. Recent developments have even allowed ratiometric quantitation of the vesicular content. This review shows that MP ultraviolet (MP-UV) microscopy is an effective but underutilized method for imaging monoamine neurotransmitters in neurones and brain tissue.

Spectrum-Resolved Triplex-Color Electrochemiluminescence Multiplexing Immunoassay with Highly-Passivated Nanocrystals as Tags

Nanocrystals (NCs) were extensively employed in optical-multiplexing with their size-dependent and narrow waveband photoluminescence (PL). Herein, to achieve NCs-based novel optical-multiplexing strategy with improved sensitivity, a spectrum-resolved triplex-color electrochemiluminescence (ECL) multiplexing immunoassay (MIA) was proposed for the first time by extensively exploring the color-different monochromatic ECL from dual-stabilizers-capped CdTe and CdSe NCs and the inherent lower background of ECL than PL. As a proof of concept, carcinoembryonic antigen (CEA), prostate specific antigen (PSA), and alpha fetoprotein (AFP) were adopted as model analytes and formed three antigen-NCs pairs at the glassy carbon electrode surface via a one-pot immune-reaction with CdSe(550), CdTe(650), and CdTe(776) NCs as tags, respectively. The spectral ECL responses of three antigen-NCs pairs were simultaneously measured via one-pot ECL assay, and the maximum ECL intensity of each tag was directly utilized to determine corresponding antigen without any assistance from either optical filters or signal deconvolution. This ECL-MIA displayed negligible cross-reactivity, high color-selectivity, and excellent sensitivity with limits of detection down to 1, 10, and 0.01 pg/mL for CEA, PSA, and AFP, respectively, which might provide a promising alternative to NCs PL multiplexing.

Current trends in the development of the electrochemiluminescent immunosensors

This review presents a general picture of the current trends and developments (2008-2013) related to electrochemiluminescence-based immunosensors. It briefly covers the milestones of qualitative changes in the field of electrochemiluminescent immunosensors; the peculiarities of the electrochemiluminescent immunoassay formats; the basic mechanisms of ECL detection, main features of early and ongoing approaches in electrochemiluminescent immunoassay commercial instruments, and the recent developments in fabrication of solid-state electrochemiluminescent immunosensors. Moreover, systematized data on biomarkers, immunoassay formats, and novel types of electrochemiluminescent label and immobilization support, such as semiconductor nanocrystals, porous noble metals, graphene, TiO2 nanotube arrays, metal-organic composites, multiwall carbon nanotubes, liposomes, photolummonescent carbone nanocrystals are presented as a table. Considerable efforts have also been devoted towards the following two key points: multiplexing analysis (multi-label, and the multianalyte strategies) and integration in microfluidic lab-on-paper devices with capabilities for point-to-care diagnostics. An immuno-like electrochemiluminescent sensor (based on synthetic receptors-molecularly imprinted polymers), as a new alternative to traditional electrochemiluminescent immunoassay is highlighted. Future perspectives and possible challenges in this rapidly developing area are also discussed.

Sandwich-type immunosensors and immunoassays exploiting nanostructure labels: A review

Methods based on sandwich-type immunosensors and immunoassays have been developed for detection of multivalent antigens/analytes with more than one eptiope due to the use of two matched antibodies. High-affinity antibodies and appropriate labels are usually employed for the amplification of detectable signal. Recent research has looked to develop innovative and powerful novel nanoparticle labels, controlling and tailoring their properties in a very predictable manner to meet the requirements of specific applications. This articles reviews recent advances, exploiting nanoparticle labels, in the sandwich-type immunosensors and immunoassays. Routine approaches involve noble metal nanoparticles, carbon nanomaterials, semiconductor nanoparticles, metal oxide nanostructures, and hybrid nanostructures. The enormous signal enhancement associated with the use of nanoparticle labels and with the formation of nanoparticle-antibody-antigen assemblies provides the basis for sensitive detection of disease-related proteins or biomolecules. Techniques commonly rely on the use of biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tag-doped nanoparticles. Rather than being exhaustive, this review focuses on selected examples to illustrate novel concepts and promising applications. Approaches described include the biofunctionalized nanoparticles, inorganic-biological hybrid nanoparticles, and signal tage-doped nanoparticles. Further, promising application in electrochemical, mass-sensitive, optical and multianalyte detection are discussed in detail.