Multiplex immunodetection of tumor markers with a suspension array built upon core–shell structured functional fluorescence-encoded microspheres

Dual-Signal-Encoded Barcodes with Low Background Signal for High-Sensitivity Analysis of Multiple Tumor Markers

The suspension array technology (SAT) is promising for high-sensitivity multiplexed analysis of tumor markers. Barcodes as the core elements of SAT, can generate encoding fluorescence signals (EFS) and detection fluorescence signals (DFS) in the corresponding flow cytometer channel. However, the bleed-through effect of EFS in the DFS channel and the reagent-driven non-specific binding (NSB) lead to background interference for ultrasensitive assay of multiple targets. Here, we report an ingenious method to eliminate background interference between barcode and reporter using low-background dual-signal-encoded barcodes (DSBs) based on microbeads (MBs) and quantum dots (QDs). The low-background DSBs were prepared via combination strategy of two signals containing scatter signals and fluorescence signals. Three types of MBs were distinguished by the scattering channel of flow cytometer (FSC vs. SSC) to obtain the scattered signals. Green quantum dots (GQDs) or red quantum dots (RQDs) were coupled to the surface of MBs by sandwich immune structure to obtain the distinguishable fluorescent signals. Furthermore, the amount of conjugated capture antibody on the MB’s surface was optimized by comparing the change of detection sensitivity with the addition of capture antibody. The combination measurements of specificity and NSB in SAT platform were performed by incubating the capture antibody-conjugated MBs (cAb-MBs) with individual QD-conjugated detection antibody (QDs-dAb). Finally, an SAT platform based on DSBs was successfully established for highly sensitive multiplexed analysis of six tumor markers in one test, which suggests the promising tool for highly sensitive multiplexed bioassay applications.

Metal Nanoparticles/MoS2 Surface-Enhanced Raman Scattering-Based Sandwich Immunoassay for α-Fetoprotein Detection

The detection of cancer biomarkers at an early stage of tumor development is vital for effective diagnosis and treatment of cancer. Current diagnostic tools can often detect cancer only when the biomarker levels are already too high, so that the tumors have spread and treatments are less effective. It is urgent therefore to develop highly sensitive assays for the detection of such biomarkers at the lowest possible concentration. In this context, we developed a sandwich immunoassay based on surface-enhanced Raman scattering (SERS) for the ultrasensitive detection of α-fetoprotein (AFP), which is typically present in human serum as a biomarker indicative of early stages of hepatocellular carcinoma. In the immunoassay design, molybdenum disulfide (MoS2) modified with a monoclonal antibody was used as a capture probe for AFP. A secondary antibody linked to an SERS-encoded nanoparticle was employed as the Raman signal reporter, that is, the transducer for AFP detection. The sandwich immunocomplex "capture probe/target/SERS tag" was deposited on a silicon wafer and decorated with silver-coated gold nanocubes to increase the density of "hot spots" on the surface of the immunosensor. The developed SERS immunosensor exhibits a wide linear detection range (1 pg mL-1 to 10 ng mL-1) with a limit of detection as low as 0.03 pg mL-1 toward AFP with good reproducibility (RSD < 6%) and stability. These parameters demonstrate that the proposed immunosensor has the potential to be used as an analytical platform for the detection of early-stage cancer biomarkers in clinical applications.

Sensitive and multiplexed detection of antibiotics using a suspension array platform based on silica-agarose hybrid microbeads

A multiplex suspension array detection platform of antibiotics has been developed based on silica-agarose hybrid microbeads (SAHMs). Chloramphenicol (CAP), sulfamethoxazole (SMX), metronidazole (MTZ) and amoxicillin (AMX) were employed as model analytes. The antigens (the antibiotics conjugated with BSA) were immobilized on the surface of four different types of SAHMs. Based on an indirect competition immunoassay, the selected antibiotics are detected through the competition of the specific monoclonal antibodies between the multiple antibiotics and the antigens. Due to high resistance to nonspecific protein absorption of SAHMs, the proposed method exhibited wide linear ranges (0.4˜72.9 ng/mL for CAP, 2.0˜108.5 ng/mL for SMX, 2.6˜142.2 ng/mL for MTZ, 1.0˜63.3 ng/mL for AMX) and low detection limits of 0.09˜0.8 ng/mL. Recoveries for spiked tap water samples were from 82% to 113%, with relative standard deviation lower than 14%, demonstrating the accuracy of the measurements performed with the developed method. This work offered a high-throughput, flexible and accurate tool, which provides a good platform for simultaneous detection of antibiotics.

Early diagnosis of disease using microbead array technology: A review

Early diagnosis of diseases (before they become advanced and incurable) is essential to reduce morbidity and mortality rates. With the advent of novel technologies in clinical laboratory diagnosis, microbead-based arrays have come to be recognized as an efficient approach, that demonstrates useful advantages over traditional assay methods for multiple disease-related biomarkers. Multiplexed microbead assays provide a robust, rapid, specific, and cost-effective approach for high-throughput and simultaneous screening of many different targets. Biomolecular binding interactions occur after applying a biological sample (such as blood plasma, saliva, cerebrospinal fluid etc.) containing the target analyte(s) to a set of microbeads with different ligand-specificities that have been coded in planar or suspension arrays. The ligand-receptor binding activity is tracked by optical signals generated by means of flow cytometry analysis in the case of suspension arrays, or by image processing devices in the case of planar arrays. In this review paper, we discuss diagnosis of cancer, neurological and infectious diseases by using optically-encoded microbead-based arrays (both multiplexed and single-analyte assays) as a reliable tool for detection and quantification of various analytes.

High-Throughput Chip Assay for Investigating Escherichia coli Interaction with the Blood-Brain Barrier Using Microbial and Human Proteome Microarrays (Dual-Microarray Technology)

Bacterial meningitis in neonates and infants is an acute lethal disease and occurs in response to microbial exploitation of the blood-brain barrier (BBB), resulting in the intracranial inflammation. Several pathogens, such as Escherichia coli ( E. coli), can cause this devastating disease; however, the underlying molecular mechanisms by which these pathogens exploit the BBB remain incompletely understood. To identify important players on both the pathogen and host sides that govern the E. coli-BBB cell interactions, we took advantage of the E. coli and human proteome microarrays (i.e., HuProt) as an unbiased, proteome-wide tool for identification of important players on both sides. Using the E. coli proteome microarrays, we developed a unique high throughput chip-based cell probing assay to probe with fluorescent live human brain microvascular endothelial cells (HBMEC, which constitute the BBB). We identified several transmembrane proteins, which effectively bound to live HBMEC. We focused on YojI protein for further study. By probing the HuProt arrays with YojI, interferon-alpha receptor (IFNAR2) was identified as one of its binding proteins. The importance of YojI and IFNAR2 involved in E. coli-HBMEC interactions was characterized using the YojI knockout bacteria and IFNAR2-knock down HBMEC and further confirmed by E. coli binding assay in HBMEC. This study represents a new paradigm (dual-microarray technology) that enables rapid, unbiased discovery of both pathogen and host players that are involved in pathogen-host interactions for human infectious diseases in a high throughput manner.

Layer-by-layer fabrication of fluorescent microspheres using micelles as a spacer: simultaneously realizing fluorescence enhancement and introduction of bioconjugation sites

Fluorescent microspheres fabricated using a conjugated polymer and micelles are demonstrated to have strong emission and are effective for bioconjugation.

Optical demodulation system for digitally encoded suspension array in fluoroimmunoassay

A laser-induced breakdown spectroscopy and fluorescence spectroscopy-coupled optical system is reported to demodulate digitally encoded suspension array in fluoroimmunoassay. It takes advantage of the plasma emissions of assembled elemental materials to digitally decode the suspension array, providing a more stable and accurate recognition to target biomolecules. By separating the decoding procedure of suspension array and adsorption quantity calculation of biomolecules into two independent channels, the cross talk between decoding and label signals in traditional methods had been successfully avoided, which promoted the accuracy of both processes and realized more sensitive quantitative detection of target biomolecules. We carried a multiplexed detection of several types of anti-IgG to verify the quantitative analysis performance of the system. A limit of detection of 1.48×10-10  M was achieved, demonstrating the detection sensitivity of the optical demodulation system.

Quantum dot-based lab-on-a-bead system for multiplexed detection of free and total prostate-specific antigens in clinical human serum samples

An immunodiagnostic lab-on-a-bead suspension microarray based on microbeads encoded with quantum dots (QDs) has been developed and preclinically validated for multiplexed quantitative detection of prostate cancer markers in human serum samples. The sensitivity and specificity of the microarray are similar to those of "gold-standard" single-analyte ELISA. Moreover, the array has an improved immunoassay capacity, ensures quantitative detection of multiple cancer biomarkers and may be operational in a considerably wider dynamic range of concentrations. The array is characterized by reduced time and cost of analysis and is compatible with classical flow cytometers. Proof-of-concept preclinical tests ensured simultaneous quantitative determination of free and total prostate-specific antigens in human serum, with clear discrimination between the control and clinical samples. The proposed approach is flexible and paves the way to development of a wide variety of immunodiagnostic assays for multiplexed early diagnosis of various diseases.

FROM THE CLINICAL EDITOR

Early diagnosis of cancer can result in better prognosis for patients. Thus, the use of specific tumor markers is widely employed in clinical practice. Traditional screening methods only employ single markers. The authors here developed a microarray system based on microbeads encoded with quantum dots (QDs), which can be used for multiplexed quantitative detection. The validated results on patient samples should lead to the development of a wider variety of assays for other diseases.

Dual tumor markers assay based on surface charged graphene

The simultaneous detection of carcinoembryonic antigen and alpha-fetoprotein was achieved by combining ionic liquid–reduced graphene oxide with two different redox probes through electrostatic adsorption.

Simple patterned nanofiber scaffolds and its enhanced performance in immunoassay

Cancer has become the leading cause of death worldwide; early diagnosis and treatment of cancers is critical for the survival of the patients. The concentration of cancer markers in easy-to-access biological fluids can provide great assistance in screening for occult primary cancers, distinguishing malignant from benign findings, determining prognosis and prediction for cancer patients. The multiplex detection technology of a panel of cancer markers can greatly increase the accuracy of disease diagnosis. Herein, we briefly fabricate a high-throughput micro-immunoassay based on the electrospun polystyrene (PS) substrates to improve detection sensitivity. The immunoassay was evaluated by analyzing three different cancer biomarkers (AFP, CEA, VEGF). For AFP, CEA, VEGF immunofluorescence assay, the LOD of assay conducted on electrospun PS substrates before or after plasma and the conventional PS substrates were 0.42, 0.10, 1.12 ng/mL, 0.57, 0.09, 1.24 ng/mL, and 159.75, 26.19, 385.59 pg/mL, respectively (P < 0.05). Due to the high porosity and large surface area-to-volume ratio which is the foremost merit of nanostructures, and the plasma treatment which make the hydrophobic PS nanofibers hydropholic, the nanofibers substrates showed sufficient retention of immunoassay functionality and high potential for capture molecules immobilization. Consequently, the immunofluorescence assay conducted on electrospun PS substrates could significantly enhance the sensitivity and limits of detection.

Protein analytical assays for diagnosing, monitoring, and choosing treatment for cancer patients

Cancer treatment is often hindered by inadequate methods for diagnosing the disease or insufficient predictive capacity regarding therapeutic efficacy. Targeted cancer treatments, including Bcr-Abl and EGFR kinase inhibitors, have increased survival for some cancer patients but are ineffective in other patients. In addition, many patients who initially respond to targeted inhibitor therapy develop resistance during the course of treatment. Molecular analysis of cancer cells has emerged as a means to tailor treatment to particular patients. While DNA analysis can provide important diagnostic information, protein analysis is particularly valuable because proteins are more direct mediators of normal and diseased cellular processes. In this review article, we discuss current and emerging protein assays for improving cancer treatment, including trends toward assay miniaturization and measurement of protein activity.

Carbon nanotube thin film biosensors for sensitive and reproducible whole virus detection

Here, we report the label-free, sensitive, and real-time electrical detection of whole viruses using carbon nanotube thin film (CNT-TF) field effect devices. Selective detection of approximately 550 model viruses, M13-bacteriophage, is demonstrated using a simple two-terminal (no gate electrode) configuration. Chemical gating through specific antibody-virus binding on CNT surface is proposed to be the sensing mechanism. Compared to electrical impedance sensors with identical microelectrode dimensions (no CNT), the CNT-TF sensors exhibit sensitivity 5 orders higher. We believe the reported approach could lead to a reproducible and cost-effective solution for rapid viral identification.

Electrochemiluminescence biosensor for the assay of small molecule and protein based on bifunctional aptamer and chemiluminescent functionalized gold nanoparticles

An electrochemiluminescence (ECL) biosensor for simultaneous detection of adenosine and thrombin in one sample based on bifunctional aptamer and N-(aminobutyl)-N-(ethylisoluminol) functionalized gold nanoparticles (ABEI-AuNPs) was developed. A streptavidin coated gold nanoparticles modified electrode was utilized to immobilize biotinylated bifunctional aptamer (ATA), which consisted of adenosine and thrombin aptamer. The ATA performed as recognition element of capture probe. For adenosine detection, ABEI-AuNPs labeled hybridization probe with a partial complementary sequence of ATA reacted with ATA, leading to a strong ECL response of N-(aminobutyl)-N-(ethylisoluminol) enriched on ABEI-AuNPs. After recognition of adenosine, the hybridization probe was displaced by adenosine and ECL signal declined. The decrease of ECL signal was in proportion to the concentration of adenosine over the range of 5.0×10(-12)-5.0×10(-9) M with a detection limit of 2.2×10(-12) M. For thrombin detection, thrombin was assembled on ATA modified electrode via aptamer-target recognition, another aptamer of thrombin tagged with ABEI-AuNPs was bounded to another reactive site of thrombin, producing ECL signals. The ECL intensity was linearly with the concentration of thrombin from 5×10(-14)M to 5×10(-10) M with a detection limit of 1.2×10(-14) M. In the ECL biosensor, adenosine and thrombin can be detected when they coexisted in one sample and a multi-analytes assay was established. The sensitivity of the present biosensor is superior to most available aptasensors for adenosine and thrombin. The biosensor also showed good selectivity towards the targets. Being challenged in real plasma sample, the biosensor was confirmed to be a good prospect for multi-analytes assay of small molecules and proteins in biological samples.