Correction: Universal control of proton concentration using an electrochemically generated acid compatible with miniaturization.

[This corrects the article DOI: 10.1039/D2NA00275B.].

Acid-Modulated Peptide Synthesis for Application on Oxide Biosensor Interfaces.

In this paper we report an acid-modulated strategy for novel peptide microarray production on biosensor interfaces. We initially selected a controlled pore glass (CPG) as a support for solid-phase peptide synthesis (SPPS) to implement a chemistry that can be performed at the interface of multiple field effect transistor (FET) sensors, eventually to generate label-free peptide microarrays for protein screening. Our chemistry uses a temporary protection of the N-terminal amino function of each amino acid building block with a tert-butyloxycarbonyl (Boc) group that can be removed after each SPPS cycle, in combination with semi-permanent protection of the side chains of trifunctional amino acid residues. Such a protection scheme with a well-proven record of application in conventional, batchwise SPPS has been fine-tuned for optimal performance on CPG and, from there, translated to SPR chips that allow layer-by-layer monitoring of amino acid coupling. Our results validate this acid-modulated synthesis as a feasible approach for producing peptides in high yields and purity on flat glass surfaces, such as those in bio-FETs.

Miniaturized Control of Acidity in Multiplexed Microreactors.

The control of acidity drives the assembly of biopolymers that are essential for a wide range of applications. Its miniaturization can increase the speed and the possibilities of combinatorial throughput for their manipulation, similar to the way that the miniaturization of transistors allows logical operations in microelectronics with a high throughput. Here, we present a device containing multiplexed microreactors, each one enabling independent electrochemical control of acidity in ∼2.5 nL volumes, with a large acidity range from pH 3 to 7 and an accuracy of at least 0.4 pH units. The attained pH within each microreactor (with footprints of ∼0.3 mm2 for each spot) was kept constant for long retention times (∼10 min) and over repeated cycles of >100. The acidity is driven by redox proton exchange reactions, which can be driven at different rates influencing the efficiency of the device in order to achieve more charge exchange (larger acidity range) or better reversibility. The achieved performance in acidity control, miniaturization, and the possibility to multiplex paves the way for the control of combinatorial chemistry through pH- and acidity-controlled reactions.

Universal control of proton concentration using an electrochemically generated acid compatible with miniaturization.

Controlling locally produced acidity in miniaturized spaces is of high importance to manage simultaneous chemical reactions. Here, we present a platform that hosts miniaturized micro-reactors each one enabling electrochemical control of the acidity in ∼nL volumes. We demonstrated the local control of chemical reactions with the deprotection of strong acid labile groups in a region of 150 µm of diameter of upstanding glass using high proton concentrations (∼10-1 M) and the acidity contrasts between the cell region and the outside. We demonstrated accurate control of the proton concentration in aqueous and organic solvents and the control of chemical reactions in organic electrolytes achieved with a sulfonated tetrafluoroethylene-based membrane, which isolates the acid generating electrodes from the reagents in the solution. The quantitative control of the acidity by faradaic currents was demonstrated by the calibration of carboxyfluorescein adjusted with external titrations and with a tautomer transition occurring at pH 4.2. To the best of our knowledge, this platform shows the best control of acidity in the smallest volume reported so far.

Mussel-Inspired Electro-Cross-Linking of Enzymes for the Development of Biosensors.

In medical diagnosis and environmental monitoring, enzymatic biosensors are widely applied because of their high sensitivity, potential selectivity, and their possibility of miniaturization/automation. Enzyme immobilization is a critical process in the development of this type of biosensors with the necessity to avoid the denaturation of the enzymes and ensuring their accessibility toward the analyte. Electrodeposition of macromolecules is increasingly considered to be the most suitable method for the design of biosensors. Being simple and attractive, it finely controls the immobilization of enzymes on electrode surfaces, usually by entrapment or adsorption, using an electrical stimulus. Performed manually, enzyme immobilization by cross-linking prevents enzyme leaching and was never done using an electrochemical stimulus. In this work, we present a mussel-inspired electro-cross-linking process using glucose oxidase (GOX) and a homobifunctionalized catechol ethylene oxide spacer as a cross-linker in the presence of ferrocene methanol (FC) acting as a mediator of the buildup. Performed in one pot, the process takes place in three steps: (i) electro-oxidation of FC, by the application of cyclic voltammetry, creating a gradient of ferrocenium (FC+); (ii) oxidation of bis-catechol into a bis-quinone molecule by reaction with the electrogenerated FC+; and (iii) a chemical reaction of bis-quinone with free amino moieties of GOX through Michael addition and a Schiff's base condensation reaction. Employed for the design of a second-generation glucose biosensor using ferrocene methanol (FC) as a mediator, this new enzyme immobilization process presents several advantages. The cross-linked enzymatic film (i) is obtained in a one-pot process with nonmodified GOX, (ii) is strongly linked to the metallic electrode surface thanks to catechol moieties, and (iii) presents no leakage issues. The developed GOX/bis-catechol film shows a good response to glucose with a quite wide linear range from 1.0 to 12.5 mM as well as a good sensitivity (0.66 µA/mM cm2) and a high selectivity to glucose. These films would distinguish between healthy (3.8 and 6.5 mM) and hyperglycemic subjects (>7 mM). Finally, we show that this electro-cross-linking process allows the development of miniaturized biosensors through the functionalization of a single electrode out of a microelectrode array. Elegant and versatile, this electro-cross-linking process can also be used for the development of enzymatic biofuel cells.

Low bioaccumulative materials for parahygrophobic nanosheets with sticking behaviour.

Here, we report the formation of surface nanosheets by electropolymerization of original 3,4 propylenedioxythiophene (ProDOT) derivatives bearing both a short perfluorobutyl chain (C4F9) and a branched alkyl chain of various lengths in order to reduce the bioaccumulative potential of the obtained materials. The dimension of the nanosheets is dependent on the size of the branched alkyl chain. These nanostructures display parahygrophobic properties (apparent contact angle θ>θ(Y) for various liquid probes, where θ(Y) is the Young angle of the corresponding smooth surface) with an extremely high liquid adhesion. These properties are due to the presence of nanoporosity between the nanosheets, which favours the Cassie-Baxter state but with high adhesion due to an important contact between the nanosheets and the liquids. These results are extremely important also in a theoretical point of view in the aim to study surfaces with high contact angles and high adhesion. Such materials could also be used in water harvesting systems especially in hot environment.