Rifampicin adsorbed onto magnetite nanoparticle: SERS study and insight on the molecular arrangement and light effect Q. S. Ferreira, a S. W. da Silva, a * C. M. B. Santos, b G. C. Ribeiro, c L. R. Guilherme c and P. C. Morais a,d In this study, the surface-enhanced Raman spectroscopy (SERS) technique was used to asses key information regarding the surface adsorption of Rifampicin (RIF) onto magnetite nanoparticle previously dressed with a bilayer of lauric acid (LA). The effects of white light illumination on the physicochemical properties of the RIF molecule were also investigated. Transmission electron microscopy, dynamic light scattering, zeta-potential, and Fourier transform infrared spectroscopy were also employed to charac- terize the investigated materials. Vibrational mode assignments for the SERS spectra and comparison between the data recorded from the free and adsorbed RIF provided insights for the adsorption of this biomolecule onto the LA-bilayer dressed magnetite nanoparticle. The results suggested that the species binding to the outer carboxylate group of the LA-bilayer is more likely the piperazine nitrogen adjacent to the imine nitrogen. The SERS data also revealed the enhancement of the RIF molecule stability to white light irradiation while adsorbed onto the magnetite nanoparticle. Copyright © 2015 John Wiley & Sons, Ltd. Additional supporting information can be found in the online version of this article at the publisher’s web site. Keywords: SERS; Rifampicin; photochemical degradation; magnetic fluid; drug delivery Introduction Rifampicin (RIF) is one of the most popular anti-tuberculosis agents belonging to the ansamycin antibiotics family. [1] Shortly, the RIF acts via the inhibition of the DNA-dependent RNA polymerase against several forms of Mycobacterium via the formation of a sta- ble enzyme-drug complex that results in suppression of the RNA chain formation. [2] However, conventional tuberculosis treatment using RIF requires high doses combined with long-term therapy. [3] Moreover, RIF presents drawbacks such as limited aqueous solubil- ity, reduced bioavailability, strong pH-dependent solubility, and re- duced stability while exposed to light. [4–7] To overcome the drawbacks presented by RIF, different nanoparticle-based drug delivery systems (DDS) have been proposed following different administration protocols, among them we can mention the liposomes, [8] the solid lipid-based and the silica-based nanoparticle. [9,10] Recently, we have shown that Amphotericin B can be adsorbed onto magnetic nanoparticles (MNPs) and suc- cessfully used in the treatment of mice’s lung infection. [11,12] There- fore, the DDS comprising the RIF adsorbed onto MNPs seems to be very much promising as a successful approach for the tuberculosis treatment. In recent years, magnetite and maghemite nanoparti- cles have been extensively explored not only with regard to their fundamental properties [13] but also because of their use in a wide range of applications, spanning from medical [14] to industrial [15] applications accounted for by the possibility of exploiting their size-dependent properties combined with reduced toxicity. Surface-functionalized MNPs suspended as a stable colloid, known as magnetic fluid (MF), has been widely used as a material platform for the biomedical applications, particularly as DDS. [16,17] However, it is extremely important to assess the physicochemical properties of the surface-functionalized MNPs in order to maximize their effi- ciency in all the aforementioned applications. Different experimental techniques, including unconventional magnetic, [18] magneto-optical [19] and optical, [20] have been used for the characterization of the MNPs suspended within the MF samples. [19,20] In this context, Raman spectroscopy has proved to be a very promising technique. Although conventional Raman spectroscopy provides important information about the chemical and structural properties of a large number of adsorbed molecules, the use of this technique in the study of the MF samples is still limited because of the strong fluorescence at low particle concen- tration or because of the small Raman cross-section. [21] However, these problems can be overcome by using the technique named surface-enhanced Raman spectroscopy (SERS) [22] that has emerged as a powerful and innovative tool in the study of the surface- adsorbed molecules in the limit of low surface grafting coefficient. * Correspondence to: S. W. da Silva, Institute of Physics, University of Brasília, Brasília, DF 70910-900, Brazil. E-mail: swsilva@unb.br a Institute of Physics, University of Brasília, Brasília, DF, 70910-900, Brazil b Department of Basic Studies and Instrumentals, State University of Southwestern Bahia, Itapetinga, Bahia, 45700-000, Brazil c State University of Goiás, CP 459, Anápolis, Goiás, 75132-903, Brazil d School of Automation, Huazhong University of Science and Technology, Wuhan 430074, China J. Raman Spectrosc. 2015, 46, 765–771 Copyright © 2015 John Wiley & Sons, Ltd. Research article Received: 9 January 2015 Revised: 22 April 2015 Accepted: 24 April 2015 Published online in Wiley Online Library: 8 June 2015 (wileyonlinelibrary.com) DOI 10.1002/jrs.4718 765