Abstract
Accuracy and speed of detection, along with technical and instrumental simplicity, are indispensable for the bacterial detection methods. Porous silicon (PSi) has unique optical and chemical properties which makes it a good candidate for biosensing applications. On the other hand, lectins have specific carbohydrate-binding properties and are inexpensive compared to popular antibodies. We propose a lectin-conjugated PSi-based biosensor for label-free and real-time detection of Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus) by reflectometric interference Fourier transform spectroscopy (RIFTS). We modified meso-PSiO2 (10–40 nm pore diameter) with three lectins of ConA (Concanavalin A), WGA (Wheat Germ Agglutinin), and UEA (Ulex europaeus agglutinin) with various carbohydrate specificities, as bioreceptor. The results showed that ConA and WGA have the highest binding affinity for E. coli and S. aureus respectively and hence can effectively detect them. This was confirmed by 6.8% and 7.8% decrease in peak amplitude of fast Fourier transform (FFT) spectra (at 105 cells mL−1 concentration). A limit of detection (LOD) of about 103 cells mL−1 and a linear response range of 103 to 105 cells mL−1 were observed for both ConA-E. coli and WGA-S. aureus interaction platforms that are comparable to the other reports in the literature. Dissimilar response patterns among lectins can be attributed to the different bacterial cell wall structures. Further assessments were carried out by applying the biosensor for the detection of Klebsiella aerogenes and Bacillus subtilis bacteria. The overall obtained results reinforced the conjecture that the WGA and ConA have a stronger interaction with Gram-positive and Gram-negative bacteria, respectively. Therefore, it seems that specific lectins can be suggested for bacterial Gram-typing or even serotyping. These observations were confirmed by the principal component analysis (PCA) model.
Highlights
Accuracy and speed of detection, along with technical and instrumental simplicity, are indispensable for the bacterial detection methods
In recent years, lectins relying on considerable properties such as low cost, desired stability, acceptable sensitivity, and selectivity has been introduced as an attractive alternative for antibodies and nucleic acids
A relatively low limit of detection (LOD) about 103 cells mL−1 was reported for WGA and ConA in their highest binding affinity profile
Summary
Accuracy and speed of detection, along with technical and instrumental simplicity, are indispensable for the bacterial detection methods. The overall obtained results reinforced the conjecture that the WGA and ConA have a stronger interaction with Gram-positive and Gram-negative bacteria, respectively It seems that specific lectins can be suggested for bacterial Gram-typing or even serotyping. Detection of bacteria by this nanostructure (PSi) is another area of research with a large number of publications in the literature[13,14] Based on these facts, in recent years, many PSi-based platforms are proposed for drug delivery, characterizing of cellular processes such as phospholipid bilayer formation and discrimination of single nucleotide changes in DNA and b ioassay[10,11,12,13]. In addition to one-dimension photonic crystal configurations of PSi, other sophisticated structures such as Bragg mirrors and microcavities have been employed for biological application[14,17,18,19]
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