Salt-Induced Control of the Grafting Density in Poly(ethylene glycol) Brush Layers by a Grafting-to Approach

In this work, a method to obtain control of the grafting density during the formation of polymer brush layers by the grafting-to method of thiolated poly­(ethylene glycol) onto gold is presented. The grafting density of the polymer chains was adjusted by adding Na₂SO₄ in concentrations between 0.2 and 0.9 M to the aqueous polymer solution during the grafting process. The obtained grafting densities ranged from 0.26 to 1.60 chains nm^–2, as determined by surface plasmon resonance. The kinetics of the grafting process were studied in situ by a quartz crystal microbalance with dissipation, and a mushroom to brush conformational transition was observed when the polymer was grafted in the presence of Na₂SO₄. The transition from mushroom to brush was only observed for long periods of grafting, highlighting the importance of time to obtain high grafting densities. Finally, the prepared brush layer with the highest grafting density showed high resistance to the adsorption of bovine serum albumin, while layers with a lower grafting density showed only limited resistance

Additional file 1 of Effects of stabilized hypochlorous acid on oral biofilm bacteria

Additional file 1. Effect of treatment with HAc on single-species biofilms of six oral bacteria. Bar charts showing mean viability ± SD (% green cells after staining with LIVE/DEAD® BacLightTM viability stain) obtained by analysis of 10 random images from each of three independent experiments for biofilms treated for 5 minutes with 25% TH broth (control) or increasing concentrations of HAc (open square = p ≤ 0.01, open triangle = p ≤ 0.0001)

Additional file 2 of Effects of stabilized hypochlorous acid on oral biofilm bacteria

Additional file 2. QCM-D data showing the shift of Δf5 values for solutions of 15% HAc (red zone, pH 2.3) and 5% HCl (green zone, pH 0.3) as a function of exposure time. White zones (R) show rinsing of the HA surface with Milli Q water

Direct Electrochemistry of Phanerochaete chrysosporium Cellobiose Dehydrogenase Covalently Attached onto Gold Nanoparticle Modified Solid Gold Electrodes

Achieving efficient electrochemical communication between redox enzymes and various electrode materials is one of the main challenges in bioelectrochemistry and is of great importance for developing electronic applications. Cellobiose dehydrogenase (CDH) is an extracellular flavocytochrome composed of a catalytic FAD containing dehydrogenase domain (DH_CDH), a heme <i>b</i> containing cytochrome domain (CYT_CDH), and a flexible linker region connecting the two domains. Efficient direct electron transfer (DET) of CDH from the basidiomycete Phanerochaete chrysosporium (<i>Pc</i>CDH) covalently attached to mixed self-assembled monolayer (SAM) modified gold nanoparticle (AuNP) electrode is presented. The thiols used were as follows: 4-aminothiophenol (4-ATP), 4-mercaptobenzoic acid (4-MBA), 4-mercaptophenol (4-MP), 11-mercapto-1-undecanamine (MUNH₂), 11-mercapto-1-undecanoic acid (MUCOOH), and 11-mercapto-1-undecanol (MUOH). A covalent linkage between <i>Pc</i>CDH and 4-ATP or MUNH₂ in the mixed SAMs was formed using glutaraldehyde as cross-linker. The covalent immobilization and the surface coverage of <i>Pc</i>CDH were confirmed with surface plasmon resonance (SPR). To improve current density, AuNPs were cast on the top of polycrystalline gold electrodes. For all the immobilized <i>Pc</i>CDH modified AuNPs electrodes, cyclic voltammetry exhibited clear electrochemical responses of the CYT_CDH with fast electron transfer (ET) rates in the absence of substrate (lactose), and the formal potential was evaluated to be +162 mV vs NHE at pH 4.50. The standard ET rate constant (<i>k</i>_s) was estimated for the first time for CDH and was found to be 52.1, 59.8, 112, and 154 s^–1 for 4-ATP/4-MBA, 4-ATP/4-MP, MUNH₂/MUCOOH, and MUNH₂/MUOH modified electrodes, respectively. At all the mixed SAM modified AuNP electrodes, <i>Pc</i>CDH showed DET only via the CYT_CDH. No DET communication between the DH_CDH domain and the electrode was found. The current density for lactose oxidation was remarkably increased by introduction of the AuNPs. The 4-ATP/4-MBA modified AuNPs exhibited a current density up to 30 μA cm^–2, which is ∼70 times higher than that obtained for a 4-ATP/4-MBA modified polycrystalline gold electrode. The results provide insight into fundamental electrochemical properties of CDH covalently immobilized on gold electrodes and promote further applications of CDHs for biosensors, biofuel cells, and bioelectrocatalysis

Effect of Deglycosylation of Cellobiose Dehydrogenases on the Enhancement of Direct Electron Transfer with Electrodes

Cellobiose dehydrogenase (CDH) is a monomeric extracellular flavocytochrome composed of a catalytic dehydrogenase domain (DH_CDH) containing flavin adenine dinucleotide (FAD), a cytochrome domain (CYT_CDH) containing heme <i>b</i>, and a linker region connecting the two domains. In this work, the effect of deglycosylation on the electrochemical properties of CDH from Phanerochaete chrysosporium (<i>Pc</i>CDH) and Ceriporiopsis subvermispora (<i>Cs</i>CDH) is presented. All the glycosylated and deglycosylated enzymes show direct electron transfer (DET) between the CYT_CDH and the electrode. Graphite electrodes modified with deglycosylated <i>Pc</i>CDH (d<i>Pc</i>CDH) and <i>Cs</i>CDH (d<i>Cs</i>CDH) have a 40–65% higher <i>I</i>_max value in the presence of substrate than electrodes modified with their glycosylated counterparts. <i>Cs</i>CDH trapped under a permselective membrane showed similar changes on gold electrodes protected by a thiol-based self-assembled monolayer (SAM), in contrast to <i>Pc</i>CDH for which deglycosylation did not exhibit any different electrocatalytical response on SAM-modified gold electrodes. Glycosylated <i>Pc</i>CDH was found to have a 30% bigger hydrodynamic radius than d<i>Pc</i>CDH using dynamic light scattering. The basic bioelectrochemistry as well as the bioelectrocatalytic properties are presented

Charge pump design.

<p>Overall scheme of the charge pump design divided into different modules connected to electronics for sensing, sampling, and wireless radio transmission of data.</p

Bench-top device test.

<p>Photographs of the set-up for the bench-top device test, showing (A) the oxygen sensitive wireless self-powered biodevice, <i>i.e.</i> an EFC (electrochemical cell containing the anodes, 1, and cathodes, 2) connected to the wireless operational unit (white box, 3) and a control device (voltmeter, 4) and (B) a computer with the developed control software and receiver (CC2530 radio highlighted with the white arrow, 5), placed roughly 4 m from the device.</p

Wireless carbohydrate sensing.

<p>Recorded signal from the carbohydrate sensitive self-contained biodevice in buffers with varying lactose concentrations.</p

Wireless oxygen sensing.

<p>Recorded signal from the self-contained biodevice for oxygen monitoring in buffers with varying oxygen concentrations.</p