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.

Hybridization chain reaction engineered DNA nanopolylinker for amplified electrochemical sensing of biomarkers

A DNA nanopolylinker was designed as a three dimensional nanoprobe with high loading of signal molecules for amplifying the biosensing signal. The nanoprobe was prepared by hybridization chain reaction engineering dsDNA polymerization on initiator DNA modified Au nanoparticle with two kinds of small molecule, for example, FITC-labeled DNA hairpins. The core-shell conjugate that was formed contained approximately 320 FITC molecules for further binding of signal molecules. With a sandwich-type immunoreaction and a biotin-streptavidin affinity reaction, the biotinylated core-shell nanoprobe was immobilized on the immunosensor surface, and the FITC molecules then bound enzyme labeled anti-FITC antibody to catalyze a silver deposition process, leading to a novel cascade signal amplification strategy. By combining the proposed strategy with stripping analysis of the deposited silver, an ultrasensitive immunoassay method for biomarker detection was developed. Under optimal conditions, this method showed a linear detection range over 5 orders of magnitude for carcinoembryonic antigen with a detection limit of 1.2 fg mL(-1) (about 18 molecules in 5.0 μL sample). The preparation of DNA nanopolylinker was simple and economic, and it could be used as a universal and multifarious probe for different bioanalytical techniques and showed the promising potential of the signal amplification strategy in the future design of biosensing methodology.

Spectrophotometric-dual-enzyme-simultaneous assay in one reaction solution: chemometrics and experimental models

Spectrophotometric-dual-enzyme-simultaneous assay in one reaction solution (SDESA) is proposed. SDESA requires the following: (a) Enzyme A acts on Substrate A to release Product A bearing the longest difference absorbance peak (λ(A)) much larger than that of Product B (λ(B)) formed by Enzyme B action on Substrate B; λ(B) is close to the longest isoabsorbance wavelength of Product A and Substrate A (λ(0)); (b) absorbance at λ(A) and λ(0) is quantified via swift alternation of detection wavelengths and corrected on the basis of absorbance additivity; (c) inhibition/activation on either enzyme by any substance is eliminated; (d) Enzyme A is quantified via an integration strategy if levels of Substrate A are lower than the Michaelis constant. Chemometrics of SDESA was tested with γ-glutamyltransferase and lactate-dehydrogenase of complicated kinetics. γ-Glutamyltransferase releases p-nitroaniline from γ-glutamyl-p-nitroaniline with λ(0) at 344 nm and λ(A) close to 405 nm, lactate-dehydrogenase consumes reduced nicotinamide dinucleotide bearing λ(B) at 340 nm. Kinetic analysis of reaction curve yielded lactate-dehydrogenase activity free from inhibition by p-nitroaniline; the linear range of initial rates of γ-glutamyltransferase via the integration strategy, and that of lactate-dehydrogenase after interference elimination, was comparable to those by separate assays, respectively; the quantification limit of either enzyme by SDESA at 25-fold higher activity of the other enzyme remained comparable to that by a separate assay. To test potential application, SDESA of alkaline phosphatase (ALP) and β-D-galactosidase as enzyme-linked-immunoabsorbent assay (ELISA) labels were examined. ALP releases 4-nitro-1-naphthol from 4-nitronaphthyl-1-phosphate with λ(0) at 405 nm and λ(A) at 458 nm, β-D-galactosidase releases 4-nitrophenol from β-D-(4-nitrophenyl)-galactoside with λ(B) at 405 nm. No interference from substrates/products made SDESA of β-galactosidase and ALP simple for ELISA of penicillin G and clenbuterol in one well, and the quantification limit of either hapten was comparable to that via a separate assay. Hence, SDESA is promising.

Integration of kinetic analysis of reaction curve with a proper classical approach for enzymatic analysis

For enzymatic analysis to quantify a substrate or enzyme, kinetic analysis of reaction curve can be integrated with a proper classical approach. For their integration, they should have consistent slopes and intercepts of linear response and an overlapped region of analyte quantities measurable under optimized conditions. To quantify a substrate after optimizations of tool enzyme activity and reaction duration, the equilibrium method works when the reaction is completed within the reaction duration; otherwise, kinetic analysis of reaction curve applies providing at least seven data with sufficient consumption of substrate. To quantify an enzyme after optimizations of initial substrate concentration and reaction duration, the classical initial rate method works when an estimated initial rate locates within the linear range; otherwise, kinetic analysis of reaction curve applies after the conversion of the quantification index with optimized parameters. This integration strategy has ideal linear ranges and practical efficiency for quantifying an enzyme at moderate substrate levels and for quantifying a substrate at moderate cost on tool enzyme; it has promise to simultaneous assays of multiple enzymes in one reaction vessel each time and ,thus, potential applications to concurrently quantify multiple serum enzymes, screen inhibitors against multiple enzyme targets, and detect multiple serum components by enzymeimmunoassay.

Two-color electrophoretic immunoassay for simultaneous measurement of insulin and glucagon content in islets of Langerhans

A multianalyte CE competitive immunoassay using two-color detection was developed to measure insulin and glucagon in islets of Langerhans. Insulin was quantified with FITC-insulin (Ins*) and anti-insulin antibodies (Ins Ab) and glucagon was quantified with Cy5-glucagon (Glu*) and anti-glucagon antibodies (Glu Ab). A 3 mW Ar(+) laser at 488 nm and a 25 mW laser diode at 635 nm were used to excite FITC and Cy5, respectively. Fluorescence was split with a half-silvered mirror and passed through a 520 +/- 20 nm bandpass filter or a 663 nm longpass filter for the detection of insulin and glucagon, respectively. The two-color detection format enabled independent quantitation of both analytes even with concentrations of insulin immunoassay reagents 20-fold higher than glucagon reagents. Simultaneous calibration curves were generated and used to determine insulin and glucagon content in islets of Langerhans. Amounts of insulin and glucagon were 56.6 +/- 3.2 and 1.0 +/- 0.5 ng/islet, respectively. LODs were 7 nM insulin and 3 nM glucagon. The assay will be applicable to fast monitoring of multiple peptides secreted from islets of Langerhans and can be applied to other systems for the quantitation of multiple analytes with large differences in concentrations.

A Disposable Multianalyte Electrochemical Immunosensor Array for Automated Simultaneous Determination of Tumor Markers

Background: Automated and convenient multianalyte detection with high throughput is increasingly needed in clinical diagnosis. We developed a disposable 4-by-2 array for programmed simultaneous amperometric immunoassay of 4 tumor markers.

Methods: We used a screen-printed technique, 1-step immobilization method, and flow injection technique. We immobilized carcinoembryonic antigen, α-fetoprotein, β-human choriogonadotropin, and carcinoma antigen 125 as model analytes in a redox mediator–grafted, biopolymer-modified, screen-printed carbon electrode array to capture corresponding horseradish peroxidase-labeled antibodies in competitive immunoreactions. The simultaneous multianalyte immunoassay was automatically carried out to amperometrically monitor the mediator-catalyzed enzymatic response to hydrogen peroxide, which decreased in proportion to the concentrations of analytes in samples.

Results: The multianalyte immunosensor array had a throughput of 60 samples/h and allowed simultaneous detection of carcinoembryonic antigen, α-fetoprotein, β-human choriogonadotropin, and carcinoma antigen 125 in clinical serum samples with concentrations up to 188 μg/L, 250 μg/L, 266 IU/L, and 334 kIU/L, respectively. The detection limits (limits of the blank, mean of blank plus 3 SD) were 1.1 μg/L, 1.7 μg/L, 1.2 IU/L, and 1.7 kIU/L. The inter- and intraassay imprecision (CVs) of the immunosensor arrays were <7.8% and <9.0%, respectively. The immunosensor arrays were stable for 28 days.

Conclusions: This newly constructed immunosensor array provides a simple, automated, simultaneous multianalyte immunoassay with high throughput, short analytical time, and sufficiently low detection limits for clinical application. This method offers the capability of miniaturizing the multianalyte detection device.

Development of dual-enzyme-based simultaneous immunoassay for measurement of progesterone and human chorionic gonadotropin

The development of a simultaneous multianalyte immunoassay for the detection of progesterone and human chorionic gonadotropin (hCG) in serum is described. In this simultaneous multianalyte assay, two different enzymes, viz. horse radish peroxidase (HRP) and alkaline phosphatase (ALP), were used as markers. To the simultaneous immobilized progesterone and hCG antibody microwells, 50 microL of different concentrations of combined standards or serum samples was added in duplicate and then 100 microL of combined conjugate reagent, composed of 17-alpha-OH-P-ALP and hCG-biotin was added to all the wells and incubated for 1h at 37 degrees C. After incubation, the contents of the wells were decanted and washed thoroughly with running tap water. After washing, 100 microL alkaline phosphatase substrate along with streptavidin-horseradish peroxidase was added to all the wells and incubated for 0.5 h at 37 degrees C. After incubation, the developed color was measured at 405 nm. The absorbency at this stage provides the result for the progesterone assay. The contents of the wells were decanted and washed. In the next step, 100 microL of tetramethylbenzidene/H2O2 reagent was added to all the wells. After 15 min of incubation, 100 microL of 0.5 M H2SO4 was added to all the wells and the color was read at 450 nm. The absorbency at this stage provides the result for the hCG assay. Sensitivity of the progesterone and hCG assays were 0.118 ng/ml and 0.124 IU/ml respectively. Intra- and inter assay percentage coefficients of variation ranged from 1.8 to 7.1 and 9.1 to 11.5 for progesterone and from 2.1 to 10.4 and 7.2 to 11.3 for hCG. There was good correlation between the discrete and the simultaneous assays. For progesterone assay, R2 was 0.99 and for hCG R2 was also 0.99. The developed dual assay for progesterone and hCG may be useful for the diagnosis of abnormal pregnancies such as miscarriages and ectopic pregnancies.