Synthesis and characterization of silver nanoparticles for biosensor design.

Transcription

1 Universidad Interamericana de Puerto Rico - Recinto de Ponce 1 Synthesis and characterization of silver nanoparticles for biosensor design. By: Pedro Rivera 1, Eulalia Medina 1 and Edmy J. Ferrer Torres 1. Science and Technology Department, Inter American University of Puerto Rico, Ponce Campus ABSTRACT The size and shape of nanoparticles plays an important role in their electrical, optical and magnetic properties. In recent years the development of simple methods for synthesis of nanoparticles has been the object of numerous studies. The core of these studies was the manufacture of nanoparticles of specific sizes that contain the desirable properties for applications. Previous work used silver nanoparticles successfully for applications in biological, technological and medical fields. Our research is focused on the synthesis of silver nanoparticles and their functionalization with biomolecules for future applications as biosensors. We describe the preparation of silver nanoparticles using several reducing agents and their interaction with a selection of biomolecules. Ascorbic Acid, Glucose, Sodium Borohydride and Sodium Citrate were the reducing agents selected for the study. The syntheses resulted in the identification of a variety of silver nanoparticles by their color and optical properties. The colors found were yellow, amber, gray and translucent. Ultraviolet-visible spectroscopy was performed to confirm the formation of silver nanoparticles. The samples absorption bands were found between 380 nm and 430 nm. The nanoparticles prepared using sodium borohydride as a reducing agent were selected to perform the interaction with the different biomolecules. The biomolecules used in our study were urea, cysteine, glycogen, dextrose and lecithin. Results obtained after the addition of the biomolecules to the nanoparticle samples showed a red shift in the Localized Surface Plasmon Resonance (LSPR). We preliminarily attribute these changes to functionalization of s with the biomolecules, but more characterization work is required to confirm this conclusion. INTRODUCTION Nanotechnology is the study, synthesis and manipulation of materials measured in nanometers. The study of nanoparticles using metal particulate like gold, silver and copper is an area of interest because of their possible applications in the area of medicine. Nanotechnology represents a tool for the improvement in our quality of life by providing a platform for new sensors or sensing element components that can be integrated into functional sensors to monitor chemicals awkward to health issues. Studies using nanoparticles and nanowires to monitor biomarkers have been object of study in the last years [1]. J. J. Mock et. al. presents a systematic study of the effect of size and shape on the spectral response of individual silver nanoparticles. They found that specific geometrical shapes give distinct spectral responses. In addition, a simple heat treatment can modify a particle shape, resulting in a change in its optical plasmon resonant properties [2]. The shape and optical properties of individual silver nanoparticles make them excellent candidates for further applications in biological assays. This study is about the effect of the concentration of amino acids on silver nanoparticle absorption. Our objective is to use Silver Nanoparticles as biosensors, adding amounts of amino acids to the Silver Nanoparticle (AgNP), and monitor changes in the LSPR (Localized Surface Plasmon Resonance).

2 Universidad Interamericana de Puerto Rico - Recinto de Ponce 2 METHODOLOGY For the preparation of the solutions utilized in the experiments described here, we used commercial silver nitrate (AgNO3), sodium borohydride (NaBH4), glucose (C6H12O6), ascorbic acid (C6H8O6), sodium citrate (C6H7NaO7), dextrose (C6H12O6), urea ( (NH2)2CO), cysteine (C3H7NO2S), lecithin and glycogen of reagent grade quality without additional purification. The solutions were prepared by dissolving the appropriate amount of the reagents with distilled water. The concentration of the solutions employed in the experiments ranged from 10-2 to 10-3 M. The s (Ag NP) were synthesized via addition of aliquots of previously stabilized silver nitrate to the solutions of different reducing agents (sodium borohydride, glucose, ascorbic acid and sodium citrate). Polyvinyl glycol (PGE) was used as the stabilizer. After the combination of the reagents, the solutions produced were heated on a hot plate or in a microwave until a change in color was obtained [3]. The formations of the s were followed through the absorption spectrum of their LSPR. UV/vis absorption spectra were recorded on a Perkin Elmer model Lambda 25 UV spectrophotometer. Following the synthesis of the Ag NP s, the interactions with the biomolecules were performed. The definition, sharpness and wavelength of the LSPR obtained were the selection criteria for the Ag NP used in the interaction with the biomolecules. The Ag NP selected was formed by the reduction with sodium borohydride. The biomolecules used were dextrose (C6H12O6), urea ((NH2)2CO), cysteine (C3H7NO2S), lecithin and glycogen. The interactions were performed by adding aliquots of the biomolecule solutions to the Ag NP. The interactions were studied by UV-vis spectroscopy. The solutions of the nanoparticles with the biomolecules were analyzed at the moment of the interaction and after a week of aging. RESULTS Synthesis of Ag NP The UV-visible absorption spectra for the Ag NP formed with the different reducing agents are summarized on Figure 1. The absorption spectra are dominated by their characteristic single band or LSPR utilized to characterize the formation of the nanoparticles. The results obtained are consistent with the UV-visible absorption spectra of Ag NP reported by previous investigators [4].The s prepared using sodium borohydride, sodium citrate and glucose show a plasmon resonance at visible region with values of 400, 415 and 420, respectively. On the other hand, s formed by reduction with ascorbic acid illustrate a plasmon resonance at UV region with a value of 300 nm. bsorbance 1.2 AgNO 3 PEG Ag NP (NaBH 4 ) Ag NP (Glucose) Ag NP (Ascorbic Acid) Ag NP (Sodium Citrate)

3 Universidad Interamericana de Puerto Rico - Recinto de Ponce 3 Figure 1. UV-visible absorption spectra of Ag NP synthesized by different reducing agents. Interaction with the biomolecules For this interaction we were seeking a precise characteristic in the nanoparticles, in particular the value of the LSPR wavelength. The wavelength desired has to be in the visible region with the highest energy possible. The nanoparticles selected were created using sodium borohydride as the reducing agent. These have the smallest LSPR wavelength value in the visible region. In addition, these Ag NP s also show higher absorption in comparison with the other two samples with wavelength in the same region. Ag + dextrose Ag + dextrose (7 days) absorbance Figure 2. UV-visible absorption spectra of Ag NP interaction with dextrose at diverse times. Figure 2 shows the absorption spectra for the interaction with dextrose. The bold line represents the absorption spectrum for the s before the interaction with dextrose. The dotted line and dashed line illustrate the absorption spectra for Ag NP after the mixing with dextrose. The dotted one was taken at the moment of mixing and the dashed one after seven days of interaction. This legend will be used to describe all graphs that illustrate absorption 600 wavelength (nm)

4 Universidad Interamericana de Puerto Rico - Recinto de Ponce 4 spectra for the interactions between the Ag NP and the biomolecules in this paper. The spectrum for the interaction with dextrose at the moment of mixing shows an increase in the absorption of the band at 400 nm. In contrast, the spectrum for the solution after seven days of the interaction shows changes in the plasmon resonance band. A small red shift of 5nm was observed. absorbance Ag + glycogen Ag + glycogen (7 days) wavelength (nm) Figure 3. UV-visible absorption spectra of Ag NP interaction with glycogen at diverse times. Figure 3 shows the absorption spectra for the interaction with glycogen. In contrast with the results obtained with dextrose, the spectrum for the interaction with glycogen at the moment of mixing shows a small red shift to greater wavelength in the plasmon resonance band. In the spectrum of the solution mixture after seven days of interaction a red shift to longer wavelength is also observed. In this sample the red shift was from 400 nm to 416 nm. Ag + cysteine Ag + cysteine (7 days) ance

5 Universidad Interamericana de Puerto Rico - Recinto de Ponce 5 Figure 4. UV-visible absorption spectra of Ag NP interaction with cysteine at diverse times. Figure 4 exhibits the absorption spectra for the interaction with cysteine. The spectrum for the interaction with cysteine at the moment of mixing shows an increase in the absorbance for the plasmon resonance band of Ag NP, the same behavior observed for the interaction between the Ag NP and dextrose. The absorption spectrum obtained in the interaction with cysteine after seven days of aging displays a red shift to higher wavelength for the LSPR band. This is the same pattern observed in the two other samples previously described. In this sample the red shift was from 400 nm to 425 nm. absorbance Ag + lecithin Ag + lecithin (7 days) wavelength (nm) Figure 5. UV-visible absorption spectra of Ag NP interaction with lecithin at diverse times. Figure 5 illustrates the absorption spectra for the interaction with lecithin. The spectra for the interaction with lecithin display the same pattern as the samples with dextrose and cysteine; there is an increase in the absorbance for the plasmon resonance band of Ag NP at

6 Universidad Interamericana de Puerto Rico - Recinto de Ponce 6 the moment of mixing and a shift to longer wavelength for the LSPR band after seven days of interaction. In this sample the red shift was from 400 nm to 410 nm. Ag + urea Ag + urea (7 days) absorbance wavelength (nm) Figure 6. UV-visible absorption spectra of Ag NP interaction with urea at diverse times. Figure 6 displays the absorption spectra for the interaction with urea. The spectrum for the interaction with lecithin shows the same pattern as the other samples for the solution obtained; however, for the interaction after seven days of aging, the sample with the Ag NP with urea doesn t show any change. This represents a change in the pattern by comparison with the interactions discussed previously. Table1. Summary of the wavelength shift observed in the Ag NP LSPR after seven days of the interaction with the biomolecules. Biomolecules Ag NP LSPR wavelength Ag NP LSPR wavelength 7 days after interaction dextrose 400 nm 405 nm glycogen 400 nm 416 nm cysteine 400 nm 425 nm Lecithin 400 nm 410 nm Urea 400 nm 400 nm As described above, positive results were obtained for the majority of the Ag NP-biomolecule interactions. Table 1 summarizes the wavelength shifts observed in the Ag NP LSPR. The greater red shift observed occurs in the Ag NP-cysteine interaction with an increase of 25 nm in wavelength for the LSPR. On the other hand, the lowest shift found has a value of 5 nm and occurs

7 Universidad Interamericana de Puerto Rico - Recinto de Ponce 7 in the Ag NP-dextrose mixture. Urea is the only biomolecule where no shift takes place. We suggest that the red shifts observed in the LSPR band absorption in the Ag NP-biomolecules interaction after seven days of aging can represent a possible functionalization of the Ag NP with the biomolecules. More experiments are needed to confirm our interpretation and to explore the most probable contact site between them. CONCLUSION s synthesized using ascorbic acid and sodium borohydride show the most defined peaks and higher intensities in their absorption spectra. Optical studies performed seven days after the mixture of the s and the biomolecules resulted in a red shift of the LSPR in the s. These observations suggest that s were successfully functionalized with several of the biomolecules. The interaction between the s and Cysteine results in the higher shift of the LSPR. The difference between them was about 26nm in comparison with dextrose, lecithin and glycogen where the shifts observed were between 10 to 15 nm. No shift was observed for the interaction between AgNP and urea. Additional experiments such as SEM, TEM and infrared spectrum analysis need to be conducted to confirm our findings and characterize our nanoparticle. ACKNOWLEDGEMENTS The authors would like to thank Dr. Ramirez Domenech and Dr. Madeline Leon Velazquez for discussions and critical review of the manuscript and to the student Anthony Lledo Torres for his collaboration in this study. Our research was supported by the Inter American University of P.R., Ponce Campus. REFERENCES 1. Ferrer, E. (2009). Fluorescence Response of CdS Nanoparticles to Serum of Cardiac Patients: towards the Development of a Real Time Sensor for Heart Failure Detection. Puerto Rico Health Science Journal. 28(3); Mock, J.J. (2002). Shape effects in plasmon resonance of individual colloidal silver nanoparticles. Journal of Chemical Physics. 116(15); Nadagouda, M., Speth T. and Varma R. (2010). Microwave-Assisted Green Synthesis of Silver Nanoparticles. Accounts of Chemical Research. 4. Guzmán, M.G., Dille, J. and Godet, S. (2008). Synthesis of silver nanoparticles by chemical reduction method and their antibacterial activity. World Academy of Science, Engineering and Technology Nadagouda, M., Speth T. and Varma R. (2008). Green Synthesis of Ag and Pd Nanospheres, Nanowires, and Nanorods Using Vitamin B2; Catalytic Polymerization of Anilline and Pyrole. Journal of Nanomaterials.

8 Universidad Interamericana de Puerto Rico - Recinto de Ponce 8 6. Kim, J., Kuk, E., Nam, K., et. al. (2007). Antimicrobial Effects of Silver Nanoparticles. Nanomedicine: Nanotechnology, Biology and Medicine Dr. Edmy J. Ferrer Torres, ejferrer@ponce.inter.edu. Ph. D. en Química Aplicada con especialidad en Materiales, M.S. en Química con concentración en Ciencia de Superficies. Especialización en Nanotecnología con énfasis en desarrollo de biosensores. Universidad de Puerto Rico-Recinto Universitario de Mayagüez. Pedro J. Rivera Pomales, pedro20126@yahoo.com, investigador subgraduado en nanotecnología, estudiante del B.S, en Ciencias Biomédicas y con concentración menor en Química, Universidad Interamericana de Puerto Rico, Recinto de Ponce Lic. Eulalia Medina, emedina@ponce.inter.edu, B.S. en Química, Pontificia Universidad Católica de P.R., Recinto de Ponce.