Abstract
Bacterial wound infections can cause septicemia and lead to limb amputation or death. Therefore, early detection of bacteria is important in chronic wound management. Here, an optical biosensor based on porous silicon resonant microcavity (pSiRM) structure modified with fluorogenic peptide substrate is demonstrated to detect the presence of Sortase A (SrtA), a bacterial enzyme found in the cell membrane protein of Staphylococcus aureus. The combination of fluorescence enhancement effects of the pSiRM architecture with the incorporation of SrtA fluorogenic peptide substrate within the pSi matrix enables the sensing of SrtA with an outstanding limit of detection of 8 × 10−14 m. Modification of the pSiRM structure with microscale spots of two fluorogenic peptide substrates, one specific for SrtA and the other for matrix metalloproteinases, effectively demonstrates the feasibility to perform multiplexed biomarker analysis. The results in this study highlight the potential of the pSiRM sensing platform as a point‐of‐care diagnostic tool for biomarkers of bacterial wound infection.
Highlights
The wound healing and cause serious infections extending into protein is important in bacterial survival during infections and the underlying bone or even systemic septicemia, with grave has been identified in S. aureus[8a] as two enzyme isoforms, Sortase A (SrtA)
The sensing platform used to detect SrtA was based on a photonic porous silicon resonant microcavity (pSiRM) structure
The enhancement in photoluminescence from the pSiRM structure is based on a spontaneous emission of the emissive substance inside the active layer of the pSiRM, which is known as the Purcell effect.[11]
Summary
The sensing platform used to detect SrtA was based on a photonic pSiRM structure. The pSiRM structure has an active cavity layer in between two distributed Bragg reflectors (DBR) of alternating high porosity (HP) and low porosity (LP) layers. The pSiRM used in this study was based on our previously reported configuration of (HP/LP)3(HP)4(LP/HP)3.[12] The HP layer was etched at a current density of 50 mA cm−2 for 2658 ms producing pore diameters ranging from 110 to 140 nm and 83.4% porosity, while the LP layer was etched at a current density of 25 mA cm−2 for 2237 ms resulting in pore diameters ranging from 40 to 60 nm and 67% porosity These conditions were designed to accommodate SrtA molecules which have unit cell dimensions of 9 nm × 9 nm × 25 nm.[13]. The refractive indices (n) were 1.3 and 1.7 for the HP and LP layers, respectively These n values combined with the λ of the designed microcavity dip were used to determine the thickness of each periodic layer considering the λ/4 rule for each DBR and λ/2 rule for the defect layer. The top view (Figure 2b) SEM image shows that the pore diameter ranged from 110 to 140 nm (the first layer or HP layer) and the cross-section (Figure 2c) SEM image shows that the thickness was around 1.4 μm, which is in agreement with the Scout simulation
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