Impact of surface wettability on S-layer recrystallization: a real-time characterization by QCM-D

Abstract

Quartz crystal microbalance with dissipation monitoring (QCM-D) has been employed to study the assembly and recrystallization kinetics of isolated SbpA bacterial surface proteins onto silicon dioxide substrates of different surface wettability. Surface modification by UV/ozone oxidation or by vapor deposition of 1H,1H,2H,2H-perfluorododecyltrichlorosilane yielded hydrophilic or hydrophobic samples, respectively. Time evolution of frequency and dissipation factors, either individually or combined as the so-called Df plots, showed a much faster formation of crystalline coatings for hydrophobic samples, characterized by a phase-transition peak at around the 70% of the total mass adsorbed. This behavior has been proven to mimic, both in terms of kinetics and film assembly steps, the recrystallization taking place on an underlying secondary cell-wall polymer (SCWP) as found in bacteria. Complementary atomic force microscopy (AFM) experiments corroborate these findings and reveal the impact on the final structure achieved.

Life under Continuous Streaming: Recrystallization of Low Concentrations of Bacterial SbpA in Dynamic Flow Conditions

“…>85% of the total mass is bound). Such an observation resembles to what has been already described by our group for stopped-flow conditions and same type of underlying substrates [19,22,24]. However, as main difference, the much larger flow rate employed in those stopped-flow experiments (300 µL/min) allowed for a faster completion of the protein adsorption (see also Supplementary Materials , Figure S1) if compared to current experiments (25 µL/min).…”

“…The assembly of a SbpA protein S-layer onto fluorinated hydrophobic SiO 2 surfaces under continuous flow conditions was initially followed by means of QCMD. This technique allows a quantitative real-time monitoring of the process in terms of bound protein mass as well as film viscous properties, according to the variations recorded for frequency (∆f ) and dissipation (∆D) factors, respectively [19]. Figure 1 depicts the results obtained for the injection of five SbpA concentrations: 100, 50, 25, 10, and 5 µg/mL.…”

“…Additionally, the analysis of the dissipation results (Figure 1, bottom) can be tackled from a similar concentration-wise perspective as the one used for frequency variations above. Thus, the highest protein concentrations employed allowed for the observation of the characteristic transition peak which sets the sudden shift towards a more elastic film, after the quite steep initial increase of the viscous properties (∆D) as the first SbpA proteins attached [19,24]. Because of the slow feeding, the usual sharp peak appeared in the shape of a broad shoulder instead.…”

“…The nanostructure of the protein layer is responsible for some of the practical properties of these biomimetic films, like its described non-fouling activity [16] of high technological usefulness [17,18]. In recent years, several studies have addressed some general questions from the assembly and recrystallization of SbpA; namely, the influence of the substrate wettability [19] or the surface chemistry [20], and the use of alternative divalent cations [21]. Recent studies have provided a more dynamic insight on the SbpA S-layer formation process in order to develop optimal crystallization models.…”

Novel biodegradable and non-fouling systems for controlled-release based on poly(ε-caprolactone)/Quercetin blends and biomimetic bacterial S-layer coatings

“…14,15 This is the case of SbpA from Lysinibacillus sphaericus CCM2177, which presents a square (p4) lattice symmetry, a system that has quite extensively been characterized in literature so far. [16][17][18] Because of the large number of nanometric pores found along the S-layer structure, it can be hypothesized that the release of the drug from the polymeric matrix can be still conducted although to a lower rate.…”