Cite this: RSC Advances, 2013, 3, 2390 Multifunctional nanoparticles for rapid bacterial capture, detection, and decontamination3 Received 25th September 2012, Accepted 7th December 2012 DOI: 10.1039/c2ra22286h www.rsc.org/advances Longyan Chen, a Fereidoon S. Razavi, b Abdul Mumin, a Xiaoxuan Guo, c Tsun- Kong Sham c and Jin Zhang* a Fluorescent magnetic nanoparticles (FMNPs) with a core–shell structure are synthesized through a one-pot chemical method followed by the bioconjugation of gentamycin (Gm). The average diameter of the FMNPs is estimated to be 65 ¡ 8 nm. The results of transmission electron microscopy (TEM), X-ray absorption near edge structure spectroscopy (XANES), and fluorospectrometry indicate that the FMNPs consist of a Fe 3 O 4 core and a fluorescent silica (SiO 2 ) shell. The FMNPs show typical superparamagnetic properties with a blocking temperature (T B ) of 120 K. We demonstrate that gentamicin (Gm)- bioconjugated FMNPs can capture gram-negative bacteria, i.e. E. coli, (1 6 10 7 CFU mL 21 from 10 mL of solution) within 20 min. TEM micrographs clearly show that the Gm-FMNPs disrupt the cell wall of E. coli prior to the lysis of E. coli as the interaction time (t) increases; whereas FMNPs without Gm are inert towards E. coli. In addition, the Gm-FMNPs are able to detect diluted E. coli cells at a concentration as low as 1 6 10 3 CFU mL 21 , which is revealed by a slight red-shift in fluorescent emissions from 517 nm to 528 nm along with a dramatic decrease in intensity. The Gm-conjugated FMNPs can be a multifunctional platform for simultaneous rapid capture, sensitive detection, and decontamination of bacteria. 1. Introduction Most bacteria, single-celled prokaryotic microorganisms, can double their population in less than 20 min, and a single bacterium can produce 10 000 cells within 4 h due to their exponential growth in the early stages of growth. 1 Escherichia coli (E. coli) is a very common gram-negative bacterium. Cases where drinking water and food have become contaminated by E. coli have been found world wide. 2 Some strains of E. coli can even cause serious bacterial infections. Antibiotics have been developed to treat bacterial infections, but the effective dosage is not well-controlled. Enzyme-linked immunosorbent assay (ELISA) and polymerase chain reaction (PCR) are normally used to detect bacteria, and this can take several days. 3,4 Consequently, the rapid capture, detection, and decontamina- tion of bacteria are needed to avoid or minimize contamina- tion of the environment, food, and infections. Engineered nanoparticles (NPs) have shown promise in applications in drug delivery, sensors, and bio-imaging. 5,6 Unlike the passive internalization of NPs within eukaryotic cells for cell tracking and drug/gene delivery, very few NPs (d , 5 nm) can penetrate the bacterial cell wall. 7–9 Therefore, well- tailored surface modification is the key to actively enhance the interaction between NPs and bacteria. Quite recently, magnetic NPs with bioconjugations that have the ability to capture bacteria have been studied. Xu and his co-workers conjugated Fe-based magnetic NPs with vancomycin, and through peptide binding captured E. coli at a low concentration of 3 6 10 4 cells mL 21 . 10 El-Boubbou et al. conjugated lectin to magnetic NPs and used mannose to bind, capture and kill E. coli. 11 Optical nanoparticles have also been applied in detecting bacteria. For instance, Zhao et al. applied fluorescent nanoparticles to quantitatively detect single bacteria. 12 Further efforts are needed to explore new biocon- jugations and advanced NPs for simultaneous rapid bacterial capture, sensitive detection, and efficient decontamination. Fluorescent magnetic nanoparticles (FMNPs) are emerging multifunctional NPs with a core–shell structure, i.e. a magnetic core coated with a fluorescent shell. The fluorescent shell can be composed of polymers and inorganic materials loaded with organic dye, 13–15 quantum dots, 16 or other complexes. 17,18 Silica is one of the well-studied materials that can act as a shell due to its functional surface, and its unique porous nature. 19–21 Previous studies demonstrated that fluorophore-loaded meso- porous SiO 2 NPs are 20 times brighter than semiconductor quantum dots. 22,23 They can be taken up by dendritic cells for cell tracking and cancer treatment. 24,25 The magnetic cores of most FMNPs are intended to be Fe 2 O 3 -rich materials. 26 a Department of Chemical & Biochemical Engineering, University of Western Ontario, London, Ontario, N6A 5B9, Canada. E-mail: jzhang@eng.uwo.ca b Department of Physics, Brock University, St. Catharines, Ontario, L2S 3A1, Canada c The Chemistry Department at the University of Western Ontario, London, Ontario, N6A 5B9, Canada 3 Electronic supplementary information (ESI) available. See DOI: 10.1039/ c2ra22286h RSC Advances PAPER 2390 | RSC Adv., 2013, 3, 2390–2397 This journal is ß The Royal Society of Chemistry 2013 Downloaded by University of Western Ontario on 20 March 2013 Published on 11 December 2012 on http://pubs.rsc.org | doi:10.1039/C2RA22286H View Article Online View Journal | View Issue