Human neutrophil elastase detection with fluorescent peptide sensors conjugated to cellulosic and nanocellulosic materials: part II, structure/function analysis

Human neutrophil elastase (HNE) is one of a number of proteases that is receiving increased attention as a marker for inflammatory diseases and sensor-based point of care diagnostics. Integral to sensor-based detection is the transducer surface, which is the platform of the sensor’s signal transmittance. Here we describe the bioactivity and related transducer surface properties of cellulose and nanocellulose matrices as peptide–cellulose fluorescent sensors. Detection sensitivity of the sensor signals for HNE levels typically found in chronic wounds is characterized. The fluorescent elastase peptide substrate, Succinamidyl-Ala-Ala-Pro-Val-amidylcoumadin (Pep) was employed in both cellulose and nanocellulose transducer surfaces evaluated for biosensor sensitivity to HNE. The cellulose transducers selected are filter paper (FP) and print cloth (PC) fabric and are comprised of processed cotton fibers. The nanocellulose transducers are the wood cellulose nanocrystals (wCNC) and the wood nanocellulose composites (wNCC). The wNCCs consist of blended quantities of nanocrystalline and microfibrillated cellulose at 66/33 and 50/50, and are characterized as thin films. The biosensor activity was in the order of wCNC-Pep > FP-Pep = NCC-Pep (50/50) > NCC-Pep (66/33) > PC-Pep. Sensor sensitivity correlated with specific surface area. A depiction of peptide substitution on nanocellulosic and cellulosic surfaces is rendered through peptide–cellulose crystallite models derived from X-ray diffraction analysis of the material, and the models discussed in light of biosensor structure activity relationships. In addition, the overall morphology, pore size and porosity of the materials are discussed for their suitability as protease sensors.