# A Photonic Label-Free Biosensor to Detect _Salmonella_ spp. in Fresh Vegetables and Meat
## 1 Introduction  
_Salmonella_ spp. can transmit infectious diseases from contaminated food and can hence seriously threaten public health [1]. _Salmonella_ is a genus of Gram-negative bacteria in the Enterobacteriaceaeze family [2; 3]. Within the _Salmonella_ genus, there are two main species: _Salmonella enterica_ and _Salmonella bongori_. This genus comprises over 2500 serotypes, each with the potential to transmit diseases in humans [4]. _Salmonella Typhimurium_ is the second most common serotype transmitted to humans, considering all foodborne pathogens [5]. A method of rapidly, selectively, and accurately detecting _Salmonella_ in consumer food products is still needed. The shallow infection limits of one colony-forming unit (CFU) of _Salmonella_ spp. in food products are regulated and reviewed under food safety laws due to the potential danger of transmission and high prevalence of _Salmonella_ spp. [3]. Commission Regulation (EC) No. 2073/2005 (amended by No. 1441/2007) requires the absence of _Salmonella_ in small quantities of food products (10 g or 25 g). Regulation No. 2073/2005 on microbiological criteria for food products states that the presence of _Salmonella_ spp. (25 g portion) constitutesa risk factor for human health. The presence of these bacteria is enough for food products to be considered unsafe. Hence, a sensitive, specific, and reliable method to detect _Salmonella_ in food products is necessary. Cultures, quantitative polymerase chain reaction (qPCR) methods, and the enzyme-linked immunosorbent assay (ELISA) are globally accepted methods for detecting _Salmonella_[6; 7; 8]. However, most must be performed by highly trained personnel using sophisticated instruments. Moreover, these methods provide false positives or negatives and are time-consuming and laborious [2]. Additionally, the sensitivity of traditional culture methods recommended by the International Organization for Standardization (ISO) under ISO standard 6579:2002 is too low to detect these bacteria [6]. Methods have been designed to identify harmful microorganisms in food such as _Salmonella_ more quickly. However, these methods cannot be validated sufficiently enough to enter the food market. Not only are they designed for specific foods and are expensive, but they also give false negatives [9]. Biosensors are now among the most recommended alternatives for rapidly detecting _Salmonella_ in food. This technology is faster, cheaper, and more portable for use in situ than existing methods. In addition, biosensors outperform multiple laboratory assays thanks to their high sensitivity, specificity, and precision [10]. In recent years, the number of biosensors being used to detect _Salmonella_ has increased. According to the International Union of Pure and Applied Chemistry (IUPAC), a biosensor is a \"self-contained integrated system that is capable of providing specific quantitative or semiquantitative analytical information using a biological recognition element that is in direct spatial contact with a transducer\" [11]. Biosensors have four main components: bioreceptor, transducer, sensor, and processor. The bioreceptor allows biological recognition of, for example, an antibody or enzyme. It is responsible for recognizing the specific analyte of interest. It is connected to a transducer. Interaction with the analyte modifies the response. The transducer's role is to convert this information into a measurable signal. This signal is then relayed to a processor for further analysis [12]. The components that enable specific, sensitive detection of _Salmonella_ spp. in a biosensor are bioreceptors. They can be any biomolecule/set that can recognize the entire bacterium or part of it [13]. The most commonly used bioreceptors to recognize _Salmonella_ include antibodies, aptamers, bacteriophages, antimicrobial peptides (AMP), and nucleic acid probes [14]. To develop a selective biosensor, recognition elements or probes must be deposited onto the immunosensor substrate for analyte identification.