Surface Enhanced Raman Spectroscopy

Surface Enhanced Raman Spectroscopy

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  1 Measurement of Glucoseby Surface Enhanced Raman Spectroscopy Nuzhet Nihaar Nasir Ahamed
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  TOPICS TO BECOVERED 2
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  Why is measuringglucose important? • To understand effect of food in blood • To manage diabetes • To help diabetic patients know their glycemic levels • To ensure safe delivery for pregnant diabetic women Glucose measurement  helps to control diabetes 3
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  Surface Enhanced RamanSpectroscopy • Principle  Raman Scattering • Raman Spectrum  obtained by directing single wavelength of light and collecting the resulting scattered light. Modern Raman Spectroscopy – A Practical Approach W.E. Smith and G. Dent 2005 John Wiley & Sons, Ltd ISBNs: 0-471-49668-5 (HB); 0-471-49794-0 (PB) Vibrational and Rotational frequencies of a molecule are characteristic of the molecule  Helps to identify the molecules 4
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  Surface Enhanced RamanSpectroscopy SERS increases intensity of Raman signal when target analyte molecules are adsorbed on the nanostructured metal substrate. 5
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  Surface Enhanced RamanSpectroscopy Why SERS? • To overcome disadvantages of Raman Spectroscopy o Underdeveloped technique o Sample degradation • Enormous increase in intensities of Raman signals • Measures adsorption of molecules on nanostructures Mechanisms of intensity enhancement • Electromagnetic enhancement - Incident light  creates localized surface plasmons  plasmon oscillates  scattering increases with perpendicular oscillations • Chemical enhancement - Incident light  Chemisorption of the surface  Charge transfer  Increases scattering 6
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  Surface Enhanced RamanSpectroscopy Instrumentation Components • monochromatic laser light source • band-pass filter • series of steering, focusing optics • collection optics • spectrometer • CCD detector Stuart, A Douglas; Walsh, T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2006, 78, 7211-7215. 7
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  Review of article1 Glucose Sensing Using Near-Infrared Surface-Enhanced Raman Spectroscopy: Gold Surfaces, 10-Day Stability, and Improved Accuracy 8
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  Review of article1 Sample Preparation Schematic of sensing surface. Preparation of Ag/Au SAM Partitioning and de-partitioning of the SAM by glucose 9 Stuart, A Douglas; Zhang, Xiaoyu, Lyandres, Olga; T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2005, 77, 4013-4019.
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  Review of article1 Reflectance spectroscopy λex = 750nm λmin for the AgFON = 738nm λmin for the AuFON = 778nm AuFON is therefore better tuned to higher λex 10 Stuart, A Douglas; Zhang, Xiaoyu, Lyandres, Olga; T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2005, 77, 4013-4019.
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  Review of article1 Electrochemical measurements CV for days 1 (black), 5 (red), and 10 (blue) on the Ag electrode CV for days 1 (black), 6 (red), and 10 (blue) on the Au electrode Percentages of current maximum vary with time SAMs are more stable and better ordered on gold than silver surfaces 11 Stuart, A Douglas; Zhang, Xiaoyu, Lyandres, Olga; T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2005, 77, 4013-4019.
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  Review of article1 SERS spectroscopy SERS Spectra Time course of the intensity to the ∼699-cm-1 peak AgFON AuFON AgFONs rapidly lost signal AuFONs remained stable for 10 days 12 Stuart, A Douglas; Zhang, Xiaoyu, Lyandres, Olga; T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2005, 77, 4013-4019.
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  Review of article1 Clarke error grid • Compare the accuracy and performance of glucose sensors in the clinically relevant range • Divided into 5 regions (A)clinically correct measurement and treatment (B) benign errors or no treatment (C) incorrect measurements leading to overcorrection of acceptable glucose levels (D)dangerous failure to detect and treat (E) treatments that further aggravate abnormal glucose levels Calibration plot Validation plot 94% of the data points in the calibration plot and 91% of data points in the prediction plot fall within the acceptable region. Stuart, A Douglas; Zhang, Xiaoyu, Lyandres, Olga; T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2005, 77, 4013-4019. 13
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  Review of article1 Conclusion • AuFONs exhibit surface plasmon resonances at longer wavelengths than similar AgFONs • SAM is more stable on the gold surface by both cyclic voltammetry and SERS spectroscopy • AuFON sensor is capable of making acceptably accurate concentration measurements even when challenged with a diverse sample population 14
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  Review of article2 Transcutaneous Glucose Sensing by Surface-Enhanced Spatially Offset Raman Spectroscopy (SESORS) in a Rat Model 15
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  Review of article2 Sample Preparation Preparation of Ag Self Assembled Monolayer 16 Yuen, M Jonathan; Shah, C Nilam; Glucksberg, R Mathew; Walsh, T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2010, 82, 8382–8385
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  Review of article2 Spectroscopic Measurement SERS spectra SESORS spectra • SERS signal is attenuated by approximately 95% due to presence of skin • But, all spectral features were easily observed with high signal to noise ratio 17 Yuen, M Jonathan; Shah, C Nilam; Glucksberg, R Mathew; Walsh, T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2010, 82, 8382–8385
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  Review of article2 Clarke error grid • 7 of the 9 validation points fell within the A and B ranges • Few deviations were observed but it was improved by increasing the number of data points in the calibration 18 Yuen, M Jonathan; Shah, C Nilam; Glucksberg, R Mathew; Walsh, T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2010, 82, 8382–8385
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  Review of article2 Conclusion Despite the numerical disparity, SERS sensor is viable in vivo and can detect glucose concentration fluctuations over time. 19 Yuen, M Jonathan; Shah, C Nilam; Glucksberg, R Mathew; Walsh, T Joseph; Duyne, Van,P Richard; Dept of Chemistry and Biomed Engg, Anal. Chem. 2010, 82, 8382–8385
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  Limitations of SERS •Large refractive index change between skin and air immediately produces intensity losses due to back reflections • Light is further attenuated due to multiple scattering and absorption within skin layers. • Placement of the SERS-active surface in vivo • The natural inflammation and foreign body response (FBR) from the human body Future Developmental Steps • Developing next generation substrates to obtain SERS signal amplification by 100 times • New surface modification strategies to improve reproducibility of SERS sensor chip • Explore modified field surfaces to expand the number of biological targets accessible to SERS 20
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  Questions? 21
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  Thank you for your kindattention 22