Elsevier

Biosensors and Bioelectronics

Volume 24, Issue 12, 15 August 2009, Pages 3399-3411
Biosensors and Bioelectronics

Review
Protein chips and nanomaterials for application in tumor marker immunoassays

https://doi.org/10.1016/j.bios.2009.03.020Get rights and content

Abstract

Recent advances in molecular biology elucidate that tumor markers play an important role in diagnosis, prognosis and providing insights into the etiology of cancer. Widespread use of tumor markers in healthcare will ultimately depend upon the detection of many tumor markers with high selectivity and sensitivity. This goal has not been obtained with conventional methods which are time-consuming, have poor precision, or experience difficulty in realizing automation. Recently, much attention has been paid to the use of electrochemical immunosensors for the detection of tumor markers due to their high sensitivity, easy miniaturization and automation. This brief review focuses on the current developments, challenges, and trends of electrochemical immunosensors for tumor markers based on protein chips. Whereafter, the recent applications of nanomaterials in tumor marker immunoassays are reviewed. We also introduce some of our group's research works of novel electrochemical immunosensors for the determination of tumor markers.

Introduction

In the tumorous process, increased levels of tumor markers in human serum are associated in patients with certain tumors. The determination of tumor markers plays an important role in the early diagnosis of cancer, differentiating benign from malignant conditions, evaluating the extent of disease, monitoring the response of tumors to therapy, and predicting recurrence. Although several research papers about tumor markers appeared in the literatures from the 1960s onwards, there are only limited kinds of tumor markers that can be used in clinical applications. Several important tumor markers are identified. Tumor markers such as carcinoembryonic antigen (CEA), carbohydrate antigen 19-9 (CA 19-9), carcinoma antigen 125 (CA 125), α-fetoprotein (AFP), prostate-specific antigen (PSA), CA 15-3 and human chorionic gonadotropin (hCG), have been widely applied for the diagnosis of colorectal cancer, pancreatic cancer, epithelial ovarian tumors and hepatocellular carcinoma, etc. Sensitive, precise, and fast multianalyte assays for measuring these protein markers in biological samples provide valuable tools in a wide range of clinical applications.

In clinical assays, the methods of detection of tumor markers in serum include radiation immunological assays (RIAs), time-resolved fluorescence, chemiluminescence, etc. But these conventional techniques have some disadvantages, such as being environmentally unfriendly, time-consuming, having poor precision, and experience difficulty in realizing automation. In some methods, the cost of specific instruments and reagents limit their wide application in clinical laboratories. Therefore, it is an urgent requirement for the development of a new immunoassay method with low-cost, high speed and real-time control in large-scale disease screening.

Immunosensors combine the advantages of sensors with high sensitivity and the immunoreactions with high specificity. Immunosensors can simultaneously monitor the progress of immunoreactions on sensor surfaces in real time, thereby providing a strong tool for the dynamic analysis of immunoreactions. There are five types of immunosensor detection device: electrochemical (amperometric, potentiometric, capacitive or impedimetric), optical (fluorescence, luminescence, refractive index (Nakamura et al., 2001, Fu et al., 2006a, Chou et al., 2004,)) microgravimetric (Zhang et al., 2007a), thermometric (Luppa et al., 2001), and immunosensors coupled with other techniques (flow injection analysis, capillary electrophoresis, etc. (Zhang et al., 2007b)). Now, immunosensors have been considered as a major development in the immunochemical field and in clinical diagnosis. Among these immunosensor devices, electrochemical devices have traditionally received the major share of attention in biosensor development. The electrochemical immunoassay has the advantages of a low detection limit, small analyte volume, simple instrumentation, and minimal manipulation, and the assay system can be easily miniaturized and integrated in protein chips. The electrochemical biosensor is applied to a molecular sensing device which intimately couples a biological recognition element to an electrode transducer. Electrochemical immunosensors convert the biological recognition event into a useful electrical signal, and produce a simple, inexpensive and yet accurate and sensitive platform for patient diagnosis. The first electrochemical immunosensor for tumor marker detection was developed in the late 1970s (Aizawa et al., 1979). The device involved a competitive assay of hCG in connection with a catalase label and amperometric monitoring of the enzymatic reaction. The development of electrochemical and chemiluminescent immunosensors for measuring tumor markers was recently reviewed by Lin and Ju (2005) and Wu et al. (2007a). The high sensitivity, specificity, simplicity, and inherent miniaturization of modern electrochemical immunosensors permit them to rival the most advanced optical methods. With the development of microfabrication and nanofabrication technology, the miniaturization allows the packing of numerous microscopic electrode transducers onto a small footprint of a biochip device, and hence the design of high-density arrays. The combination of electrochemical immunosensors and protein chips promotes the detection of tumor markers towards high sensitivity, high throughput and low sample consumption. Moreover, the application of nanomaterials such as gold nanoparticles (AuNPs), Si nanowires and carbon nanotubes plays an important role in the signal amplification and designs of protein chips.

Here, this brief review focuses on the reported electrochemical immunosensors of tumor markers based on protein chips and nanomaterials for clinical applications. At the same time, we also introduce some of our group's recent research works on electrochemical immunosensors for tumor marker detection.

Section snippets

Protein chips-based immunosensors

Protein chips have become crucial tools for high throughput and large-scale bioassays, and they have been applied to the analysis of antigen–antibody reactions, protein–protein interactions and drug discovery, etc. (Kersten et al., 2003, Liao et al., 2006, Lueking et al., 2005, Zhu and Snyder, 2003). Protein chips consist of immobilized biomolecules spatially addressed on planar substrates such as glass or silicon slides. Immobilized biomolecules, here referred to as probes, usually include

Nanoparticles

In the last few years, nanoparticles research has received much attention because such materials frequently display unusual physical (structural, electronic, magnetic and optical) and chemical properties (catalytic, biocompatible). Nanoparticles provide a particularly useful platform for bioanalysis, drug delivery, clinical diagnosis, etc. Nanoparticles, such as gold colloids, magnetic nanoparticles and quantum dots (QDs), have been widely used for designing immunoassays for tumor markers based

Antibody related issues

The assay performance depends now more on the availability of antibody (Ab) with high affinity constants and low cross-reactivity. There are two kinds of antibodies, polyclonal and monoclonal, depending on the way they are prepared. Polyclonal Ab has higher sensitivity and lower specificity as compare to monoclonal Ab. Therefore, during selecting a monoclonal Ab or polyclonal Ab, all factors including specificity, sensitivity, cross-reactivity and costs should be considered. Fortunately, some

Conclusions

As described previously, electrochemical immunosensors constructed on protein chips have made prominent progress in the detection of tumor markers and also play an important role in the early diagnosis of cancer. Particularly, the miniaturization and integration of electrochemical detection systems on microarray chips may allow multianalyte detection for application in point-of-care cancer diagnosis. The high sensitivity of modern electrochemical bioaffinity assays should facilitate early

Acknowledgments

We gratefully acknowledge the financial support from the National Nature Science Foundation of China (Grant Nos.: 20805009, 20525519, 90606014, 20890020), SRF for ROCS, SEM, Shanghai Leading Academic Discipline Project (B109 & 08XD14010) and Shanghai Nature Science Foundation (08ZR1400900).

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