Biosensors, Nanosensors and Biochips: Frontiers in Environmental and Medical Diagnostics

This presentation describes three areas of research related to the development of biosensors, nanosensors and biochips for chemical, biological and medical analysis: (1) nanostructured plasmonics-based probes for surface-enhanced Raman scattering (SERS) biochemical analysis, and (2) nanosensors for in vivo analysis of a single cell and (3) multifunctional biochips for medical diagnostics. INTRODUCTION The field of photonics has recently experienced an explosive growth due to the non-invasive or minimally invasive nature and the costeffectiveness of biophotonic modalities in environmental sensing, medical diagnostics and therapy [1]. This lecture discusses the development and application of advanced biomedical photonics, molecular spectroscopy, biosensors and biochips for environmental and biomedical diagnostics. PLASMONIC-BASED NONOPROBES The first research area involves the development of plasmonic nanoprobes having enhanced electromagnetic properties of metallic nanostructures. The term plasmonics is derived from “plasmons”, which are the quanta associated with longitudinal waves propagating in matter through the collective motion of large numbers of electrons. Incident light irradiating these surfaces excites conduction electrons in the metal, and induces excitation of surface plasmons leading to enormous electromagnetic enhancement for ultrasensitive detection of spectral signatures: surface-enhanced Raman scattering (SERS) and surface-enhanced fluorescence (SEF). Raman spectroscopy has proven to be an effective technique as an analytical tool. This is partly due to its non-destructive nature and structural fingerprinting capability with very narrow and highly resolved bands (0.1 nm). In addition, the spectral measurement is rapid and requires little sample preparation, which gives it the potential for on-line analysis and field applications. However, conventional Raman spectroscopy suffers from low sensitivity and often requires powerful and expensive lasers for excitation. In the mid-to-late 1970s, it was discovered that when molecules were adsorbed onto specific solid substrates, an enhanced Raman signal of the adsorbate was obtained with intensity enhancements of 10-10. This effect has since become known as surfaceenhanced Raman scattering (SERS) spectroscopy [2]. The SERS enhancement is thought to be the result of a combination of intense localized fields arising from surface plasmon resonance in metallic nano-structures and chemical effects. The exact nature of the SERS phenomenon is still under intense investigation [6-8]. The intensity of the normally weak Raman scattering process is increased by factors as large as 10-10 for compounds adsorbed onto a SERS substrate, allowing for trace-level detection. Fig. 1 shows a scanning electron micrograph (SEM) of a SERS–active nanospheres (300-nm diameter coated with a 100-nm layer of silver). Our nanoparticle-based SERS technology that has enabled sensitive detection of a variety of compounds of environmental and medical interest. The SERS nanoprobe technology has also been incorporated in several fiberoptic probe designs for remote analysis. The development of a SERS gene probe technology based on the solid surface-based technology has also been reported. In one study, the selective detection of HIV DNA and cancer gene was demonstrated [3]. Figure 1: SEM photograph of Silver-Coated Nanosphere-based SERS substrates The 1 International Symposium on Micro & Nano Technology, 14-17 March, 2004, Honolulu, Hawaii, USA 2 During the last decade, our laboratory has been interested in the development of optical techniques for genomics analysis due to the strong interest in non-radioactive DNA probes for use in biomedical diagnostics, pathogen detection, gene identification, gene mapping and DNA sequencing. We have focused on not only the development of efficient SERS-active solid substrates for trace organic analysis in biological and environmental applications [4] but also the development of SERS-active solid substrates for biomedical diagnostics. We have developed SERS gene probes to detect the human BLC2 gene, which is an important representative of a family of cancer genes. Due to their non-radioactive nature, there is strong interest in the development of optical techniques for biomedical diagnostics, pathogen detection, gene identification, gene mapping and DNA sequencing. The hybridization of a nucleic acid to its complementary target is one of the most definite and well-known molecular recognition events. Therefore, the hybridization of a nucleic acid probe to its DNA target can provide a very high degree of accuracy for identifying complementary DNA sequences [24]. OPTICAL NANOSENSORS Biology has entered a new era with the recent advances in nanotechnology, which have recently led the development of biosensor devices having nanoscale dimensions that are capable to probe the innerspace of single living cells. Nanosensors provide new and powerful tools for monitoring in vivo processes within living cells, leading to new information on the inner workings of the entire cell [5, 6]. Such a systems biology approach could greatly improve our understanding of cellular function, thereby revolutionizing cell biology. Fiberoptic sensors provide useful tools for remote in situ monitoring. Fiberoptic sensors could be fabricated to have extremely small sizes, which make them suitable for sensing intracellular/intercellular physiological and biological parameters in microenvironments. A wide variety of fiberoptic chemical sensors and biosensors have been developed in our laboratory for environmental and biochemical monitoring [1]. We have developed nanosensors for in situ intracellular measurements of single cells using antibody-based nanoprobes. In this work, we describe the development of nano-biosensors for in situ monitoring of single cells using biosensors having antibody-based nanoprobes having 40-nm diameter (Fig. 2). Figure 2 Photograph of an Antibody-based Nanoprobe. (The small size of the probe (200nm diameter) allows manipulation of the nanoprobe at specific locations within single cells). Figure 3 Photograph of Single Cell Sensing Using the Nano-Biosensor. Fig. 3 shows a photograph of an antibody-based nanoprobe used to measure the presence of BPT inside a single cell. The small size of the nanoprobe allowed it to be manipulated to specific locations within the Clone 9 cells. Tip ~ 40 nm