Search

An optical fiber based immunosensing platform formed by two identical chirped long period gratings (CLPGs) for sensitive and label-free detection of Escherichia coli (E. coli) is presented. The proposed immunosensor having two CLPGs with an inter-grating space (IGS) works like a Mach-Zehnder interferometer. The important feature of this sensor is that by changing the refractive index (RI) induced phase at the IGS region, a corresponding shift in resonance wavelength can be realized without affecting the actual grating region. Additionally, the confining bandwidth of the interference fringes promotes greater resolution in the resonance wavelength analysis of the transmission spectrum. The main aim of this study was the specific and rapid detection of the E. coli bacteria in phosphate buffer saline (detection range: 10 cfu/ml to 60 cfu/ml) by using the bio-functionalized IGS region as a sensing probe of the dual CLPG structure. The observed detection limit was 7 cfu/ml. For specificity analysis, Salmonella typhimurium and Staphylococcus aureus were tested and no significant shift in resonance wavelength was observed. In addition, the proposed immunosensor has the ability to selectively detect E. coli in real samples including lake water. The high specificity, good sensitivity to ambient RI, and robustness of the developed sensing platform will open a new avenue in optical immunosensing technology, and cascaded long CLPG sensors can contribute significantly to the detection of pathogenic bacteria in water and food samples. [ABSTRACT FROM AUTHOR]

Abstract The molybdenum disulfide (MoS 2) nanosheets functionalized fiber optic surface plasmon resonance (SPR) immunosensor has been reported for the sensitive detection of Escherichia coli (E. coli). The MoS 2 nanosheets were prepared by chemical exfoliation method. The synthesised nanostructures were characterized for their structural, morphological and optical properties. The E. coli monoclonal antibodies were successfully immobilized on the MoS 2 functionalized sensing platform via hydrophobic interactions. An alternative method simplifying the antibodies immobilization process by functionalization of 2D nanomaterial (MoS 2 nanosheets) for rapid (~15 mins) bacterial quantification is presented in this study. The immunosensor uses wavelength interrogation method and a strong linear relationship (R2 = 0.994) was observed between spectral response of immunosensor and different concentration of E. coli. The nonspecificity and cross-reactivity studies of the developed immunosensor were investigated with detection of Salmonella Typhimurium and Staphylococcus aureus. To demonstrate the practical application, spiked samples of water and orange juice were analysed with acceptable recovery results. The label-free immunosensor exhibits better performance, detection limit (94 CFU/mL), high sensitivity (2.9 nm/1000 CFU mL−1; 3135 nm/RIU) and profound specificity as compared to conventional fiber optic SPR sensor (detection limit: 391 CFU/mL, sensitivity: 0.6 nm/1000 CFU mL−1; 1646 nm/RIU). This sensing platform shows promising applications in regular water and food quality monitoring for various pathogenic microorganisms. Graphical abstract fx1 Highlights • A fiber optic SPR immunosensor with functionalized MoS 2 nanosheets is reported. • 2D MoS 2 nanosheets improved the SPR immunosensor sensitivity (LOD: 94 CFU/mL). • Selectivity analysis of the developed immunosensor was investigated. • The developed method offers simple bio-functionalization and rapid quantification. • For practicality, spiked samples of drinking water and orange juice were tested. [ABSTRACT FROM AUTHOR]

Graphical abstract Highlights • Label-free detection of S. Typhimurium by SMS structure with LOD of 247 CFU/mL. • Sensing principle is based on multimode interference for S. Typhimurium detection. • Specific quantification of S. Typhimurium in presence of E. coli and S. aureus. • Advantages of simple fabrication and good sensitivity (275.86 nm/RIU). Abstract A label-free fiber optic biosensor based on single mode-tapered multimode-single mode (SMS) structure for bacteria detection has been reported. The main aim of the present study was the sensitive detection of Salmonella Typhimurium in phosphate buffer saline (PBS) and spiked samples of milk. The multimode interference based SMS sensor was developed for biosensing application by removal of cladding region of the multimode fiber, followed by modification of the etched region with anti- S. Typhimurium monoclonal antibodies. The antibodies functionalized SMS biosensor provided S. Typhimurium detection in a wide linear range (500 CFU/mL − 5000 CFU/mL) to attain limit of detection (LOD) of 247 CFU/mL. The complete analysis process for each sample including regeneration was completed in less than 20 min. A comprehensive theoretical study of the developed biosensor regarding beam propagation and power distribution has been presented. The developed biosensor showed high selectivity in the presence of Escherichia coli and Staphylococcus aureus. It provides an alternative platform for rapid and specific detection of S. Typhimurium without any prior sampling processes. The proposed biosensing technique could be used for sensitive detection (275.86 nm/RIU) of the broad spectrum of pathogens. [ABSTRACT FROM AUTHOR]