Hsl 800_review.docx

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Study of Biosensing Applications of Non Plasmonic Materials using SERS Detection Sarjana Yadav(2018PHZ8331) Indian Institute of Technology, Delhi

Introduction Surface Enhanced Raman Spectroscopy (SERS) have been used as a promising technique for biomolecular sensing due to its sensitivity to single molecule detection and enormous enhancement of Raman signals for the molecules of interest. In last several decades there has been an exclusive study on plasmonics using nanostructure made up of noble metals (Au, Ag, Cu etc.). However inspite of their high plasmonic properties these metals suffer from several limitations such as high optical losses, high cost, poor in vitro biocompatibliy and selectivity. These shortcomings have motivated the researchers to look for alternative materials with similar properties but overcoming the limitations of regular plasmonic metals. Recently several studies have been carried out using materials like aluminium, graphene, Oxide of semiconductors such as Zinc Oxide and Indium Oxide with these materials showing a good SERS enhancement. ZnO based 3D semiconductor has been recently studied for in vitro cancer diagnosis [1]. Graphene due to its low loss, high confinement, excellent optical properties and good tunablity has recently come up as a promising plasmonic material as an alternative to noble metals [2]. However little work has been done to explore its biocompatibility in SERS detection. Since the non plasmonic materials have shown poor response at the nanoscale so the work done yet mostly involves either the reduction of the material to quantum scale enhancing the ability for SERS response or by combining these with the metal nanoparticles enhancing the SERS effect. The Oxide semiconductors can be highly doped to make them conducting films and this is what provides them metal like properties in the optical region. The optical properties of these semiconductors can be tuned by changing the carrier concentration and hence these can be grown in thin films and nanostructures forming an alternative

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for Plasmonic metals. Heavily doped Indium Tin Oxide (ITO) and Zinc Oxide (ZnO) have been experimentally proven to be good candidates for plasmonic applications [3]. Moreover due to their high biocompatibility these materials can be functionalized with different biomolecules similar to gold and silver nanoparticles.

Discussion In the work done for early detection of cancer using ZnO based SERS response, invitro cancer diagnosis was performed since ZnO quantum structures showed high biocompatibility with both Zn+2 and O2- ions getting dissolved in the cells. The low SERS enhancement of these semiconductor based structures can be enhanced due to vibrational coupling between surface defects like oxygen vacancies and molecules, and charge transfer. The ZnO based probes demonstrated the SERS enhancement factor of nearly the order of 106 which can be considered high for non-plasmonic materials. The work presents a well driven mechanism for formation and characterization of ZnO based semiconductor quantum probes with the probes decorated on nano dendrite platform weakly bonded to them so that the probes can be easily adhered to the cells. The SERS excitations showing maximum enhancement at 785 nm for Crystal Violet, Rhodamine-6G, 4ATP and 4MBA was confirmed. The enhanced SERS signals were studied successfully for cancerous and non cancerous cells with cellular internalization of quantum probes for different time intervals and a discrimination between the two was done using multivariate Principal Component Analysis (PCA) and discriminant analysis. In addition to Enhanced Raman Sensitivity, the quantum probes unlike the traditional plasmonic metals (Au, Ag) showed excellent cell adherence because of its structural similarity with extracellular matrix. Another non plasmonic 2 dimensional material showing high advantage compared to conventional metal plasmonic materials is graphene. Great achievements in graphene plasmonics has been made theoretically and experimentally. Graphene provides us a powerful Raman spectra and there has been reports of microanalysis of other molecules with the effects of enhancement from Graphene substrate which has been named as Graphene enhanced Raman Scattering (GERS). However, graphene also like

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other non plasmonic materials has limitation of low enhancement factor and limits its use as a sensitive enhancement substrate. Therefore work has been reported to improve the SERS effect by combining metal nanoparticles and graphene. An appreciable increment in enhancement has been observed for graphene covered with gold or silver nanoparticles. Another advantage provided by graphene is that it suppresses photoluminescence background giving clearer results. Use of graphene in biodetection has been reported where SERS detection of Folic Acid has been performed using graphene oxide/silver nanoparticles [4]. It suggests the hybridisation of silver nanoparticles and graphene oxide to enhance the electronic and optical properties of the hybrid and the interaction of graphene oxide with the target molecules has been utilized to improve the sensitivity of biomedical detection. Therefore, corresponding to the enrichment of folic acid molecules on the graphene oxide and strong SERS activity exhibited by the hybrid due to Ag nanoparticles, label free detection of Folic acid by SERS spectra had been studied.

Conclusion In most of the work reported so far, the enhancement of non plasmonic semiconductor oxides has been increased using methods like size confinement or changing the dielectric properties of these oxides [5]. To explore this field of research combination of the conventional plasmonic metals with non plasmonic semiconductor oxides can be done to study and observe the corresponding enhancement in SERS spectra. An increase in enhancement can be expected due to strong SERS activity shown by Ag, Au metals and at the same time a high biocmpatibity due to the suitable non plasmonic material can be expected. Also from the work done yet using graphene as a plasmonic material, the further strategy which may be worked upon can be setting graphene sheet on the top of the metal plasmonic structures such that electromagnetic field of the metal can be passed through graphene sheet enhancing the Raman signal and making it good choice for SERS . The flat graphene surface and its stability may help to provide clean, stable and reproducible signal.

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References [1] R. Haldavnekar, K. Venkatakrishna, B. Tan. Non plasmonic semiconductor quantum SERS probe as a pathway for in vitro cancer detection, Nature Communications, 2018, 9, 3065. [2] X Luo, T. Qiu, W Lu, Z Ni, Plasmons in graphene: Recent progress and applications. [3] G.V. Naik, V.M. Shalaev, A. Boltaseva. Alternative Plasmonic Materials: Beyond Gold and Silver, Adv. Mater.,2013, 25, 3264-3294. [4] W. Ren, Y. Feng, E. Wang, A Binary Functional Substrate for Enrichment and Ultrasensitive SERS Spectroscopic Detection of Folic Acid Using Graphene Oxide/Ag Nanoparticle Hybrids, ACS Nano, 2011, 8, 6425-6433. [5] S.K. Mishra, B.D. Gupta, Surface Plasmon Resonance-Based Fiber-Optic Hydrogen Gas Sensor Utilizing Indium–Tin Oxide (ITO) Thin Films, 2012, Plasmonics, 7, 627-632.