Amperometric micro-immunosensor for the detection of tumor biomarker

Simultaneous Electrochemical Detection of LDL and MDA-LDL Using Antibody-Ferrocene or Anthraquinone Conjugates Coated Magnetic Beads

The simultaneous detection of atherosclerotic cardiovascular disease (ACSVD) biomarkers was recently of great scientific interest. In this work, magnetic beads-based immunosensors for the simultaneous detection of low density lipoprotein (LDL) and malondialdehyde-modified low density lipoprotein (MDA-LDL) were presented. The approach proposed was based on the formation of two types of specific immunoconjugates consisting of monoclonal antibodies: anti-LDL or anti-MDA-LDL, together with redox active molecules: ferrocene and anthraquinone, respectively, coated on magnetic beads (MBs). The decrease in redox agent current in the concentration range: 0.001-1.0 ng/mL for LDL and 0.01-10.0 ng/mL for MDA-LDL, registered by square wave voltammetry (SWV), was observed upon the creation of complex between LDL or MDA-LDL and appropriate immunoconjugates. The detection limits of 0.2 ng/mL for LDL and 0.1 ng/mL for MDA-LDL were estimated. Moreover, the results of selectivity against the possible interferents were good, as human serum albumin (HSA) and high density lipoprotein (HDL), stability and recovery studies demonstrated the potential of platform proposed for early prognosis and diagnosis of ASCVD.

Biogenic carbon dot-based fluorescence-mediated immunosensor for the detection of disease biomarker

The dynamic interplay of nanotechnology and immunoassay has unlocked an arena for developing next-generation techniques to contribute to detecting disease biomarkers. Herein, the work establishes the strategic fabrication of an immunosensor by sandwich technique based on the fluorescence phenomenon of carbon dots for the detection of the disease biomarker VEGF (Vascular Endothelial Growth Factor). VEGF, a biomarker for angiogenesis, is considered cancerous if found in elevated levels in the blood, and so is paramount for early detection of disease. Carbon dots derived from a biogenic source were synthesized employing a green microwave-assisted method followed by conjugating with a detection antibody, human immunoglobulin G (IgG), via EDC-NHS amidation reaction. On the other hand, the VEGF biomarker was immobilized onto the capture antibody. The detection antibody tagged with the fluorescent probe is employed as a bridge to connect with the VEGF biomarkers bound to the capture antibody. The response to different concentrations of VEGF biomarkers was recorded in terms of the fluorescence intensity of the carbon dots. The fluorescence immunosensor could exhibit a wide linear range of 0.1 fg/mL to 10 pg/mL with a low detection limit of 5.65 pg/mL towards VEGF. The potentiality of this designed immunosensor was qualitatively assessed with human blood plasma samples, showing promising results, thereby upholding the applicability of carbon dots as fluorescent labels in immunoassay techniques.

Current Update on Biomarkers for Detection of Cancer: Comprehensive Analysis

Early and effective diagnosis of cancer is decisive for its proper management. In this context biomarker-based cancer diagnosis is budding as one of the promising ways for early detection, disease progression monitoring, and effective cancer therapy. Integration of Biosensing devices with different metallic/nonmetallic nanoparticles offers amplification and multiplexing capabilities for simultaneous detection of cancer biomarkers (CB's). This study provides a comprehensive analysis of the most recent designs and fabrication methodologies designed for developing electrochemical biosensors (EB) for early detection of cancers. The role of biomarkers in cancer therapeutics is also discussed.

Antibody–Ferrocene Conjugates as a Platform for Electro-Chemical Detection of Low-Density Lipoprotein

Low-density lipoprotein (LDL) is a cardiac biomarker identified in the pathology of cardiovascular disease (CVD). Typically, the level of LDL is calculated using the Friedewald relationship based on measured values of total cholesterol, high-density lipoproteins (HDL), and triglycerides. Unfortunately, this approach leads to some errors in calculation. Therefore, direct methods that can be used for fast and accurate detection of LDL are needed. The purpose of this study was to develop an electrochemical platform for the detection of LDL based on an antibody–ferrocene conjugate. An anti-apolipoprotein B-100 antibody labeled with ferrocene was covalently immobilized on the layer of 4-aminothiophenol (4-ATP) on the surface of gold electrodes. Upon interaction between LDL and the antibody–ferrocene conjugate, a decrease in the ferrocene redox signal registered by square wave voltammetry was observed, which depends linearly on the concentration from 0.01 ng/mL to 1.0 ng/mL. The obtained limit of detection was equal to 0.53 ng/mL. Moreover, the satisfied selectivity toward human serum albumin (HSA), HDL, and malondialdehyde-modified low-density lipoprotein (MDA-LDL) was observed. In addition, the acceptable recovery rates of LDL in human serum samples indicate the possible application of immunosensors presented in clinical diagnostics.

Novel electrochemical PMI marker biosensor based on quantum dot dissolution using a double-label strategy

A novel and facile post-mortem interval (PMI) biosensor was fabricated using a double-label strategy to detect the glyceraldehyde 3-phosphate dehydrogenase (GAPDH) biomarker. A monoclonal anti-GAPDH antibody was immobilized on a surface label containing cadmium selenide quantum dots (CdSe QDs) on a cysteamine graphene oxide (Cys-GO) self-assembled monolayer. Glucose oxidase (GOx) was used as a signal label to conjugate with GAPDH. GAPDH recognition was achieved through the dissolution of the surface-attached CdSe QDs by hydrogen peroxide generated through GAPDH-conjugated GOx-catalyzed β-glucose oxidation. To enhance sensitivity, a competitive interaction was introduced between free and conjugated GAPDH to the active site of the anti-GAPDH antibody. The electrochemical response due to CdSe dissolution decreased proportionally with the concentration of free GAPDH. Differential pulsed voltammetry was conducted to determine the analytical characteristics of the immunosensor, including the limit of detection, linear dynamic range, target selectivity, system stability, and applicability toward the analysis of real samples.

Integrated electrochemical microfluidic sensor with hierarchically porous nanoarrays modified graphene fiber microelectrode for bioassay

The development of high-efficient biosensing systems for rapid and sensitive detection of disease-related biomarkers in human samples is of great significance for disease diagnosis and treatment in clinical practice. In this work, we develop an integrated electrochemical microfluidic sensing platform based on freestanding graphene fiber (GF) microelectrode for bioassay. In order to improve the electrocatalytic activity of GF microelectrode, it has been modified by unique 3D well-ordered hierarchically porous nickel-cobalt phosphide (NiCoP) nanosheet arrays (NSAs). Benefiting from the excellent electrochemical properties and structural merits, the resultant NiCoP-NSAs modified GF microelectrode shows excellent sensing performances towards neurotransmitter dopamine (DA), with a high sensitivity of 5.56 μA cm^-2 μM^-1, a low detection limit of 14 nM, as well as good selectivity, reproducibility and stability. Furthermore, in virtue of the miniaturized size and good mechanical properties, the nanohybrid GF microelectrode can be embedded into a home-made microfluidic chip to construct an integrated electrochemical microfluidic sensing device, which has been used for sensitive analysis of DA in minimal volume of human serum and urine samples, and in situ tracking DA released from neuroblastoma cells SHSY-5Y under the stimulation for physio-pathological and pharmacological study of nervous system-related diseases.

Development of a functional impedimetric immunosensor for accurate detection of thyroid-stimulating hormone

Thyroid-stimulating hormone (TSH), which regulates the synthesis of thyroid gland hormones affecting the whole metabolism, is a pituitary hormone. Determination of TSH is crucial for monitoring thyroid gland-related disorders and some metabolic diseases.In this study, a nonlabeled immunosensor based on covalent immobilization of anti-TSH antibody by using the formation of self-assembled monolayers (SAM) of 4-mercaptophenylacetic acid (4-MPA) and functionalization of carboxyl ends with 1-ethyl-3-(3-dimetilaminopropil) carbodiimide (EDC)/N-Hydroxysuccinimide (NHS) was fabricated for detection of TSH. Immobilization steps including the concentration of 4-MPA, the concentration of anti-TSH antibody, and duration of anti-TSH antibody incubation were optimized by utilizing electrochemical impedance spectroscopy. Under optimal conditions, a sensitive, rapid, and accurate determination of TSH at a concentration range between 0.7 and 3.5 mIU/L was accomplished with a notable linearity and LOD value of 0.034 mIU/L, as well as reproducibility and repeatability. Moreover, for comparison, linear range experiments were also carried out by using other electrochemical methods, including linear sweep voltammetry, cyclic voltammetry, and capacitance spectroscopy. Finally, the constructed immunosensor was used for analyzing TSH levels spiked in the artificial serum samples.

Strategies for Biomolecular Analysis and Continuous Physiological Monitoring

Portable devices capable of rapid disease detection and health monitoring are crucial to decentralizing diagnostics from clinical laboratories to the patient point-of-need. Although technologies have been developed targeting this challenge, many require the use of reporter molecules or reagents that complicate the automation and autonomy of sensors. New work in the field has targeted reagentless approaches to enable breakthroughs that will allow personalized monitoring of a wide range of biomarkers on demand. This Perspective focuses on the ability of reagentless platforms to revolutionize the field of sensing by allowing rapid and real-time analysis in resource-poor settings. First, we will highlight advantages of reagentless sensing techniques, specifically electrochemical detection strategies. Advances in this field, including the development of wearable and in situ sensors capable of real-time monitoring of biomarkers such as nucleic acids, proteins, viral particles, bacteria, therapeutic agents, and metabolites, will be discussed. Reagentless platforms which allow for wash-free, calibration free-detection with increased dynamic range are highlighted as a key technological advance for autonomous sensing applications. Furthermore, we will highlight remaining challenges which must be overcome to enable widespread use of reagentless devices. Finally, future prospects and potential breakthroughs in precision medicine that will arise as a result of further development of reagentless sensing approaches are discussed.

A highly-sensitive vascular endothelial growth factor-A(165) immunosensor, as a tool for early detection of cancer

Biomarkers can be ideal indicators for assessing the risk of the presence of a disease. In this study, a label-free electrochemical biosensor was designed to quantify the vascular endothelial growth factor A (165) (VEGF-A(165)) antigen, using reduced graphene oxide-gold nanoparticle for early detection of breast cancer. The conductivity of gold nanoparticle along with its biocompatibility provide an enhanced surface, suitable for anti-VEGF antibody immobilization. 11-mercaptoundecanoic acid was used to facilitate a single-step and convenient bonding of the antibodies to the surface, compared to previous studies. The dynamic range of the biosensor was between 20 to 120 pg/ml and its limit of detection of the biomarker VEGF-A(165) was obtained to be about 0.007 pg/ml, using different electric signal transduction modes. Hence, the biosensor is a beneficial immunosensor with high sensitivity and ideal dynamic range for early-stage diagnosis of breast cancer and other cancers diseases associated with expression of VEGF-A(165). The as-prepared immunosensor could be efficiently employed for designing a point-of-care diagnostic platform.

Recent advances in aptamer-based sensors for breast cancer diagnosis: special cases for nanomaterial-based VEGF, HER2, and MUC1 aptasensors

Cancer is one of the most common and important diseases with a high mortality rate. Breast cancer is among the three most common types of cancer in women, and the mortality rate has reached 0.024% in some countries. For early-stage preclinical diagnosis of breast cancer, sensitive and reliable tools are needed. Today, there are many types of biomarkers that have been identified for cancer diagnosis. A wide variety of detection strategies have also been developed for the detection of these biomarkers from serum or other body fluids at physiological concentrations. Aptamers are single-stranded DNA or RNA oligonucleotides and promising in the production of more sensitive and reliable biosensor platforms in combination with a wide range of nanomaterials. Conformational changes triggered by the target analyte have been successfully applied in fluorometric, colorimetric, plasmonic, and electrochemical-based detection strategies. This review article presents aptasensor approaches used in the detection of vascular endothelial growth factor (VEGF), human epidermal growth factor receptor 2 (HER2), and mucin-1 glycoprotein (MUC1) biomarkers, which are frequently studied in the diagnosis of breast cancer. The focus of this review article is on developments of the last decade for detecting these biomarkers using various sensitivity enhancement techniques and nanomaterials.

Antibody-Electroactive Probe Conjugates Based Electrochemical Immunosensors

Suitable immobilization of a biorecognition element, such as an antigen or antibody, on a transducer surface is essential for development of sensitive and analytically reliable immunosensors. In this review, we report on (1) methods of antibody prefunctionalization using electroactive probes, (2) methods for immobilization of such conjugates on the surfaces of electrodes in electrochemical immunosensor construction and (3) the use of antibody-electroactive probe conjugates as bioreceptors and sensor signal generators. We focus on different strategies of antibody functionalization using the redox active probes ferrocene (Fc), anthraquinone (AQ), thionine (Thi), cobalt(III) bipyridine (Co(bpy)33+), Ru(bpy)32+ and horseradish peroxidase (HRP). In addition, new possibilities for antibody functionalization based on bioconjugation techniques are presented. We discuss strategies of specific, quantitative antigen detection based on (i) a sandwich format and (ii) a direct signal generation scheme. Further, the integration of different nanomaterials in the construction of these immunosensors is presented. Lastly, we report the use of a redox probe strategy in multiplexed analyte detection.

Electrochemical immunoassay for the detection of stress biomarkers

A rapid electrochemical immunoassay method was developed to detect and measure stress biomarkers (cortisol and cortisone) in two biological samples (Zebrafish whole-body and artificial saliva). This methodology utilizes an immunoassay approach taking advantage of the lock and key mechanism that is related to the antibody-antigen interaction depending on the reliable immobilization of the antibody labelled with ferrocene tags (Ab-Fc) on a modified tin-doped indium oxide (ITO) electrode using electrochemical instrumentation to build a POC platform. The limit of detection (LOD) obtained for this biosensor was 1.03 pg ml⁻¹ for cortisol and 0.68 pg ml⁻¹ for cortisone, respectively. The correlation coefficient was 0.9852 and 0.9841 for cortisol and cortisone, respectively with a linear concentration from (0-50 ng ml⁻¹) which covers the standard levels of stress hormones in both selected biological samples. The incubation time was investigated and 30 min was found to be the optimum incubation time. This time would be acceptable for the POC system as total process time can be determined within 35 min.

Flexible Biosensors for the Impedimetric Detection of Protein Targets Using Silk-Conductive Polymer Biocomposites

To expand the applications of flexible biosensors in point-of-care healthcare applications beyond monitoring of biophysical parameters, it is important to devise strategies for the detection of various proteins and biomarkers. Here, we demonstrate a flexible, fully organic, biodegradable, label-free impedimetric biosensor for the critical biomarker, vascular endothelial growth factor (VEGF). This biosensor was constructed by photolithographically patterning a conducting ink consisting of a photoreactive silk sericin coupled with a conducting polymer. These functional electrodes are printed on flexible fibroin substrates that are controllably thick and can be free-standing, or conform to soft surfaces. Detection was accomplished via the antibody to VEGF which was immobilized within the conducting matrix. The results indicated that the developed flexible biosensor was highly sensitive and selective to the target protein, even in challenging biofluids such as human serum. The biosensors themselves are biocompatible and degradable. Through this work, the developed flexible biosensor based on a simple and label-free strategy can find practical applications in the monitoring of wound healing or early disease diagnosis.

Microbiological Sensing Technologies: A Review

Microorganisms have a significant influence on human activities and health, and consequently, there is high demand to develop automated, sensitive, and rapid methods for their detection. These methods might be applicable for clinical, industrial, and environmental applications. Although different techniques have been suggested and employed for the detection of microorganisms, and the majority of these methods are not cost effective and suffer from low sensitivity and low specificity, especially in mixed samples. This paper presents a comprehensive review of microbiological techniques and associated challenges for bioengineering researchers with an engineering background. Also, this paper reports on recent technological advances and their future prospects for a variety of microbiological applications.

Hydrogel-based suspension array for biomarker detection using horseradish peroxidase-mediated silver precipitation

Advances in medical diagnostics and personalized therapy require robust, sensitive yet cost-effective diagnostic tools for rapid measurement of biomolecules including proteins in body fluids. State-of-the-art technologies are complex and rely on expensive or custom made detection system, and therefore, cannot be readily adapted for point-of-care (POC) analysis. The development of a novel detection platform, which leverages horseradish peroxidase (HRP)-mediated silver precipitation within antibody immobilized porosity tuned poly (ethylene) glycol diacrylate (PEGDA) hydrogel microparticles with the operational advantages of suspension arrays for sensitive quantification of biomarkers, is described. In this study, vascular endothelial growth factor (VEGF) has been used as a model protein. The silver deposition corresponded to the concentration of VEGF in solution. The detection limit of 5.2 ± 1.0 pg/mL and assay time of 2 h highlights that this assay exceeds the conventional technologies in terms of sensitivity and speed. The practical applicability of the hydrogel microparticle based detection system has been established by demonstrating the ability of the system to quantify the production of VEGF by highly aggressive (MDA-MB-231) and non-aggressive (MCF-7) breast cancer cells. The reliance on simple instrument for quantification of clinically relevant markers bolsters the adaptability of the detection platform/method in POC settings.

Recent advances in biosensor development for the detection of cancer biomarkers

Cancer is the second largest disease throughout the world with an increasing mortality rate over the past few years. The patient's survival rate is uncertain due to the limitations of cancer diagnosis and therapy. Early diagnosis of cancer is decisive for its successful treatment. A biomarker-based cancer diagnosis may significantly improve the early diagnosis and subsequent treatment. Biosensors play a crucial role in the detection of biomarkers as they are easy to use, portable, and can do analysis in real time. This review describes various biosensors designed for detecting nucleic acid and protein-based cancer biomarkers for cancer diagnosis. It mainly lays emphasis on different approaches to use electrochemical, optical, and mass-based transduction systems in cancer biomarker detection. It also highlights the analytical performances of various biosensor designs concerning cancer biomarkers in detail.

Biosensors for breast cancer diagnosis: A review of bioreceptors, biotransducers and signal amplification strategies

Breast cancer is highly prevalent in females and accounts for second highest number of deaths, worldwide. Cumbersome, expensive and time consuming detection techniques presently available for detection of breast cancer potentiates the need for development of novel, specific and ultrasensitive devices. Biosensors are the promising and selective detection devices which hold immense potential as point of care (POC) tools. Present review comprehensively scrutinizes various breast cancer biosensors developed so far and their technical evaluation with respect to efficiency and potency of selected bioreceptors and biotransducers. Use of glycoproteins, DNA biomarkers, micro-RNA, circulatory tumor cells (CTC) and some potential biomarkers are introduced briefly. The review also discusses various strategies used in signal amplification such as nanomaterials, redox mediators, p19 protein, duplex specific nucleases (DSN) and redox cycling.

Microelectromechanical System-Based Sensing Arrays for Comparative in Vitro Nanotoxicity Assessment at Single Cell and Small Cell-Population Using Electrochemical Impedance Spectroscopy

The traditional in vitro nanotoxicity assessment approaches are conducted on a monolayer of cell culture. However, to study a cell response without interference from the neighbor cells, a single cell study is necessary; especially in cases of neuronal, cancerous, and stem cells, wherein an individual cell's fate is often not explained by the whole cell population. Nonetheless, a single cell does not mimic the actual in vivo environment and lacks important information regarding cell communication with its microenvironment. Both a single cell and a cell population provide important and complementary information about cells' behaviors. In this research, we explored nanotoxicity assessment on a single cell and a small cell population using electrochemical impedance spectroscopy and a microelectromechanical system (MEMS) device. We demonstrated a controlled capture of PC12 cells in different-sized microwells (to capture a different number of cells) using a combined method of surface functionalization and dielectrophoresis. The present approach provides a rapid nanotoxicity response as compared to other conventional approaches. This is the first study, to our knowledge, which demonstrates a comparative response of a single cell and small cell colonies on the same MEMS platform, when exposed to metaloxide nanoparticles. We demonstrated that the microenvironment of a cell is also accountable for cells' behaviors and their responses to nanomaterials. The results of this experimental study open up a new hypothesis to be tested for identifying the role of cell communication in spreading toxicity in a cell population.

A universal strategy for aptamer-based nanopore sensing through host-guest interactions inside α-hemolysin

Nanopore emerged as a powerful single-molecule technique over the past two decades, and has shown applications in the stochastic sensing and biophysical studies of individual molecules. Here, we report a versatile strategy for nanopore sensing by employing the combination of aptamers and host-guest interactions. An aptamer is first hybridized with a DNA probe which is modified with a ferrocene⊂cucurbit[7]uril complex. The presence of analytes causes the aptamer-probe duplex to unwind and release the DNA probe which can quantitatively produce signature current events when translocated through an α-hemolysin nanopore. The integrated use of magnetic beads can further lower the detection limit by approximately two to three orders of magnitude. Because aptamers have shown robust binding affinities with a wide variety of target molecules, our proposed strategy should be universally applicable for sensing different types of analytes with nanopore sensors.

Sensitive, quantitative, and high-throughput detection of angiogenic markers using shape-coded hydrogel microparticles

Demonstration of the application of shape coded hydrogel microparticles for multiplexed detection of angiogenic molecules. Utilization of single fluorophore eliminates the spectral overlap associated with microparticle based multiplexed analysis.

Live cell integrated surface plasmon resonance biosensing approach to mimic the regulation of angiogenic switch upon anti-cancer drug exposure

In this work, we report a novel surface plasmon resonance (SPR) based live-cell biosensing platform to measure and compare the binding affinity of vascular endothelial growth factor (VEGF) to vascular endothelial growth factor receptor (VEGFR) and VEGF to bevacizumab. Results have shown that bevacizumab binds VEGF with a higher association rate and affinity compared to VEGFR. Further, this platform has been employed to mimic the in vivo condition of the VEGF–VEGFR angiogenic switch. Competitive binding to VEGF between VEGFR and bevacizumab was monitored in real-time using this platform. Results demonstrated a significant blockage of VEGF–VEGFR binding by bevacizumab. From the results, it is evident that the proposed strategy is simple and highly sensitive for the direct and real-time measurements of bevacizumab drug efficacy to the VEGF–VEGFR angiogenic switch in living SKOV-3 cells.

Designing label-free electrochemical immunosensors for cytochrome c using nanocomposites functionalized screen printed electrodes

We have designed here a label-free direct electrochemical immunosensor for the detection of cytochrome c (cyt c), a heme containing metalloprotein using its specific monoclonal antibody. Two nanocomposite-based electrochemical immunosensor platforms were evaluated for the detection of cyt c; (i) self-assembled monolayer (SAM) on gold nanoparticles (GNP) in polypyrrole (PPy) grafted screen printed electrodes (SPE) and (ii) carbon nanotubes (CNT) integrated PPy/SPE. The nanotopologies of the modified electrodes were confirmed by scanning electron microscopy. Electrochemical impedance spectroscopy and cyclic voltammetry were employed to monitor the stepwise fabrication of the nanocomposite immunosensor platforms. In the present method, the label-free quantification of cyt c is based on the direct electron transfer between Fe (III)/Fe (II)-heme redox active site of cyt c selectively bound to anti-cyt c nanocomposite modified SPE. GNP/PPy and CNT/PPy nanocomposites promoted the electron transportation through the conductive pore channels. The overall analytical performance of GNP/PPy based immunosensor (detection limit 2 nM; linear range: 2 nM to 150 µM) was better than the anti-cyt c/CNT/PPy (detection limit 10 nM; linear range: 10 nM to 50 µM). Further, the measurement of cyt c release in cell lysates of cardiomyocytes using the GNP/PPy based immunosensor gave an excellent correlation with standard ELISA.

Three-dimensional hierarchical plasmonic nano-architecture enhanced surface-enhanced Raman scattering immunosensor for cancer biomarker detection in blood plasma

A three-dimensional (3D) hierarchical plasmonic nano-architecture has been designed for a sensitive surface-enhanced Raman scattering (SERS) immunosensor for protein biomarker detection. The capture antibody molecules are immobilized on a plasmonic gold triangle nanoarray pattern. On the other hand, the detection antibody molecules are linked to the gold nanostar@Raman reporter@silica sandwich nanoparticles. When protein biomarkers are present, the sandwich nanoparticles are captured over the gold triangle nanoarray, forming a confined 3D plasmonic field, leading to the enhanced electromagnetic field in intensity and in 3D space. As a result, the Raman reporter molecules are exposed to a high density of "hot spots", which amplifies the Raman signal remarkably, improving the sensitivity of the SERS immunosensor. This SERS immunosensor exhibits a wide linear range (0.1 pg/mL to 10 ng/mL) and a low limit of detection (7 fg/mL) toward human immunoglobulin G protein in the buffer solution. This biosensor has been successfully used for detection of the vascular endothelial growth factor in the human blood plasma from clinical breast cancer patient samples.

Characterization of three amino-functionalized surfaces and evaluation of antibody immobilization for the multiplex detection of tumor markers involved in colorectal cancer

Antibody microarrays are powerful and high-throughput tools for screening and identifying tumor markers from small sample volumes of only a few microliters. Optimization of surface chemistry and spotting conditions are crucial parameters to enhance antibodies' immobilization efficiency and to maintain their biological activity. Here, we report the implementation of an antibody microarray for the detection of tumor markers involved in colorectal cancer. Three-dimensional microstructured glass slides were functionalized with three different aminated molecules ((3-aminopropyl)dimethylethoxysilane (APDMES), Jeffamine, and chitosan) varying in their chain length, their amine density, and their hydrophilic/hydrophobic balance. The physicochemical properties of the resulting surfaces were characterized. Antibody immobilization efficiency through physical interaction was studied as a function of surface properties as well as a function of the immobilization conditions. The results show that surface energy, steric hindrance, and pH of spotting buffer have great effects on protein immobilization. Under optimal conditions, biological activities of four immobilized antitumor marker antibodies were evaluated in multiplex immunoassay for the detection of the corresponding tumor markers. Results indicated that the chitosan functionalized surface displayed the highest binding capacity and allowed to retain maximal biological activity of the four tested antibody/antigen systems. Thus, we successfully demonstrated the application of amino-based surface modification for antibody microarrays to efficiently detect tumor markers.

Detection of single tumor cell resistance with aptamer biochip

In this study, a novel RNA aptamer biochip was developed for tumor cell capture and detection of single cell resistance. This biochip consists of a polydimethylsiloxane (PDMS) cover containing a channel for introducing cells and sustaining their activity and microelectrode matrix on a silicon dioxide layer. Epidermal growth factor receptor (EGFR) aptamers which specifically identify and isolate tumor cells were attached in the gap between two electrodes. After cell biochip incubation, surplus tumor cells were removed, and those dwelling on the intervals were further analyzed. When resistance measurement was completed, these cells were flushed away via controlled flow acceleration, and were collected for further analysis. The results demonstrate the convenience and efficiency of using anti-EGFR aptamer biochips for the detection of single cell resistance. This novel aptamer biochip may be used for the isolation of circulating tumor cells from peripheral blood and cell counting, or be assembled with other lab-on-a-chip components for follow-up gene and protein analysis.

Optical aptasensors for the analysis of the vascular endothelial growth factor (VEGF)

The vascular endothelial growth factor, VEGF, is an important biomarker for different diseases and clinical disorders. We present a series of optical aptasensor-based sensing platforms for VEGF that include the following: (i) A FRET-based sensor that involves the VEGF-induced separation of aptamer-functionalized quantum dots blocked by a quencher nucleic acid (detection limit 1 nM). (ii) A FRET-based sensor based on the VEGF-induced assembly of the aptamer subunits functionalized with QDs and a dye acceptor (Cy5), respectively (detection limit 12 nM). (iii) A chemiluminescence aptasensor based on VEGF-induced assembly of a hemin/G-quadruplex catalyst (detection limit 18 nM). (iv) A chemiluminescence aptasensor based on the VEGF-stimulated assembly of two aptamer subunits into the hemin/G-quadruplex catalyst (detection limit 2.6 nM). (v) A chemiluminescence resonance energy transfer (CRET) aptasensor based on the VEGF-induced assembly of a semiconductor QDs-hemin/G-quadruplex supramolecular structure (detection limit 875 pM). Furthermore, an amplified optical aptasensor system based on the Exonuclease III (Exo III) recycling of the VEGF analyte was developed. In this system, one aptamer subunit is modified at its 5' and 3' ends with QDs and a black hole quencher, respectively. The VEGF-induced self-assembly of the aptamer subunits result in the digestion of the quencher units and the autonomous recycling of the analyte, while triggering-on the luminescence of the QDs (detection limit 5 pM). The system was implemented to analyze VEGF in human sera samples.