Thermal Stability of Phage Peptide Probes Vs. Aptamer for Salmonella Detection on Magnetoelastic Biosensors Platform
Authors: Chen I-Hsuan , Horikawa Shin , Du Songtao , Liu Yuzhe , Wikle Howard Clyde , Barbaree James M , Chin Bryan A 
Published: February 2020

According to CDC, Salmonella enterica spp. is one of the major food pathogens commonly associated with outbreaks in United States. A rapid sensor test for Salmonella detection is essential to improve and monitor food safety procedures. Magnetoelastic (ME) sensors have been recently developed as a novel, real-time, and wireless platform for Salmonella typhimurum detection in food systems (Horikawa et al., 2015). The sizes of the ME sensors are only a few millimeters or less, and are freestanding ME resonators that are very cost efficient after microfabrication. The performance of this ME biosensor relies on the adhesion characteristics of the bio-recognition probes coating on the sensor surface through Au deposition, and they also rely on the probe’s binding affinity to bacterial targets for low Salmonella detection. When a time-varying magnetic field is applied, the ME biosensors can be placed into mechanical resonance by magnetostriction. Upon the attachment of the target pathogen to the bio-recognition probes on the sensor, a resonant frequency shift of this sensor occurs to give a positive detection signal. Therefore, a good affinity and stable bio-recognition probe is essential for this ME biosensor platform.

Environmental monitoring, such as monitoring food pathogens in poultry processing plant with heat and humidity requires thermostable probes. A thermal stable probe can maintain its sensitivity and specificity to the target pathogens when the environment temperature is not favored.

Antibodies, phage peptides, and aptamers (DNA/RNA) are three major groups of bio-recognition molecules currently used in the pathogen detection fields. Even though antibodies are known to bind to bacteria targets with good affinity and specificity, antibody-based assays have several environmental limitations, including not holding their structures under high temperature conditions. Phage peptides are engineered and developed through a process called biopanning selection using phage display methods. After selecting the good affinity phage peptide to its target, the whole phage with this peptide can be used directly on the sensor platform. These phages, called filamentous phages, are known to survive in hard environments, like high temperatures. Petrenko et al, (2005) reported that phage-derived probes bind to biological agents and generate detectable signals at the temperatures of 63°C. Aptamers are short synthetic molecules that can comprise of nucleic or amino acid (DNA in this study) and commonly selected through SELEX procedures (Systematic Evolution of Ligands by Exponential Enrichment). There are studies showed that aptamers are more effective than antibodies for target binding at higher temperatures. However, there is no study comparing the affinity of phages vs. aptamers to a target pathogen in various thermo-conditions.

In this study, the affinity of phage probes vs. aptamers to Salmonella enterica Typhimurium at various thermal conditions was evaluated using ELISA (Enzyme Link Immunosorbent Assay) tests. DNA aptamers were able to perform Salmonella detection at 50⁰C. When the temperature was increased to 60⁰C, the aptamers’ detection signals dropped down to baseline. Phage probes showed good thermal stabilities for Salmonella detection when the temperature was increased to 60⁰C. To our knowledge, this is the first report of a comparison study of phages vs aptamers used for pathogen detection.