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a microfluidic nano-biosensor for the detection of pathogenicsalmonellagiyoung kimn , ji-hea moon, chang-yeon moh, jong-guk limnational academy of agricultural science, department of agricultural engineering, rda, 150 suin-ro, kweonseonku, suwon 441-100, republic of koreaa r t i c l e i n f oarticle history:received 3 june 2014received in revised form28 july 2014accepted 15 august 2014available online 19 august 2014keywords:microfluidicsnano-biosensorfood safetysalmonella typhimuriuma b s t r a c trapid detection of pathogenic salmonella in food products is extremely important for protecting thepublic from salmonellosis. the objective of the present study was to explore the feasibility of using amicrofluidic nano-biosensor to rapidly detect pathogenic salmonella. quantum dot nanoparticles wereused to detect salmonella cells. for selective detection of salmonella, anti-salmonella polyclonalantibodies were covalently immobilized onto the quantum dot surface. to separate and concentratethe cells from the sample, superparamagnetic particles and a microfluidic chip were used. a portablefluorometer was developed to measure the fluorescence signal from the quantum dot nanoparticlesattached to salmonella in the samples. the sensitivity for detection of pathogenic salmonella wasevaluated using serially diluted salmonella typhimurium in borate buffer and chicken extract. thefluorescence response of the nano-biosensor increased with increasing cell concentration. the detectionlimit of the sensor was 10 3 cfu/ml salmonella in both borate buffer and food extract.& 2014 elsevier b.v. all rights reserved.1. introductioncontamination of food with pathogens poses a significantthreat to public health. recent foodborne pathogen outbreaksfrom various food sources have increased public awareness ofthese pathogens. salmonella is a major foodborne pathogen andsalmonella typhimurium is the one of the most commonlyreported serotypes. s. typhimurium is a gram-negative rod thatcauses self-limiting gastroenteritis in humans, and infection isassociated with symptoms of fever, abdominal pain, nausea andvomiting, diarrhea, dehydration, weakness, and loss of appetite.the symptoms may appear 12–72 h after consumption of acontaminated food or beverage. the pathogen is associated withraw or undercooked eggs, poultry, beef, and unwashed fruit. s.typhimurium outbreaks continue to occur, and outbreaks fromvarious food sources have increased the need for simple, rapid,and sensitive methods to detect foodborne pathogens.conventional methods for salmonella detection and identifica-tion involve multiple, prolonged enrichment steps. although someimmunological rapid assays are available, these assays still requireenrichment steps and give results in 18–48 h. enzyme-linkedimmunoassay (elisa) and polymerase chain reaction (pcr) arerobust but require several lengthy steps, expensive laboratoryinstruments, and experienced operators (hart et al., 2011;hossain et al., 2012). biosensing methods, such as optical(kramer et al., 2007), impedimetric (radke and alocilja, 2004;varshney and li, 2007; yang et al., 2004), electrochemical(setterington and alocilja, 2012), and piezoelectric (campbelland mutharasan, 2008) methods, have shown great potential forrapid detection of foodborne pathogens.among biosensing methods, fluorescent dye-based opticalimmunoassays have been widely used because they can be highlysensitive and simple to operate (geng et al., 2004; kim et al., 2007;kramer and lim, 2004). however, methods that rely on organicfluorescent dyes are limited by their sensitivity to photobleaching,which limits long-term analysis. they also have a narrow excita-tion bandwidth and overlapping emission profiles from differentfluorophores, which limits multiplexed applications (kampaniet al., 2007). recently developed nanotechnology has the potentialto overcome the limitations of organic fluorophores. fluorescentnanoparticles and quantum dots (qds) have several advantagesover conventional organic dyes, such as high quantum yield andbrightness, photostability, and resistance to chemical degradation.semiconductor qds exhibit size- and composition-dependentfluorescence properties that are suitable for multi-target andhighly sensitive imaging using single excitation wavelengths(tallury et al., 2010). the water solubility of qds makes themsuitable for biological applications, including imaging, detection,and biomolecular conjugation. several groups have reported theapplication of qds for detection of microorganisms, includingescherichia coli o157:h7 (su and li, 2004; wang et al., 2012; zhuet al., 2012), campylobacter jejuni (bruno et al., 2009), listeriacontents lists available at sciencedirectjournal homepage: www.elsevier.com/locate/biosbiosensors and bioelectronicshttp://dx.doi.org/10.1016/j.bios.2014.08.0230956-5663/& 2014 elsevier b.v. all rights reserved.n corresponding author. tel.: þ82 31 290 1899; fax: þ82 31 290 1900.e-mail address: giyoung@korea.kr (g. kim).biosensors and bioelectronics 67 (2015) 243–247