Multifunctional Encoded Self-Assembling Protein Nanofibrils as Platform for High-Throughput and Multiplexed Detection of Biomolecules

A highly sensitive nanopore platform for measuring RNase A activity

Ribonuclease A (RNase A) plays significant roles in several physiological and pathological conditions and can be used as a valuable diagnostic biomarker for human diseases such as myocardial infarction and cancer. Hence, it is of great importance to develop a rapid and cost-effective method for the highly sensitive detection of RNase A. The significance of RNase A assay is further enhanced by the growing attention from the biotechnology and pharmaceutical industries to develop RNA-based vaccines and drugs in large part as a result of the successful development of mRNA vaccines in the COVID-19 pandemic. Herein, we report a label-free method for the detection of RNase A by monitoring its proteolytic cleavage of an RNA substrate in a nanopore. The method is ultra-sensitive with the limit of detection reaching as low as 30 fg per milliliter. Furthermore, sensor selectivity and the effects of temperature, incubation time, metal ion, salt concentration on sensor sensitivity were also investigated.

Functionalized Prion-Inspired Amyloids for Biosensor Applications

Protein amyloid nanofibers provide a biocompatible platform for the development of functional nanomaterials. However, the functionalities generated up to date are still limited. Typical building blocks correspond to aggregation-prone proteins and peptides, which must be modified by complex and expensive reactions post-assembly. There is high interest in researching alternative strategies to tailor amyloid-based nanostructures’ functionality on demand. In the present study, the biotin-streptavidin system was exploited for this purpose. Prion-inspired heptapeptides (Ac-NYNYNYN-NH₂, Ac-QYQYQYQ-NH₂, and Ac-SYSYSYS-NH₂) were doped with biotin-conjugated counterparts and assembled into amyloid-like fibers under mild conditions. The scaffolds’ versatile functionalization was demonstrated by decorating them with different streptavidin conjugates, including gold nanoparticles, quantum dots, and enzymes. In particular, they were functionalized with peroxidase or phosphatase activities using streptavidin conjugated with horseradish peroxidase and alkaline phosphatase, respectively. Modification of amyloid-like nanostructures has generally been restricted to the addition of a single protein moiety. We functionalized the fibrils simultaneously with glucose oxidase and horseradish peroxidase, coupling these activities to build up a nanostructured glucose biosensor. Overall, we present a simple, modular, and multivalent approach for developing amyloid-based nanomaterials functionalized with any desired combination of chemical and biological moieties.

Multifunctional Electrochemical Platforms Based on the Michael Addition/Schiff Base Reaction of Polydopamine Modified Reduced Graphene Oxide: Construction and Application

In this paper, a new strategy for the construction of multifunctional electrochemical detection platforms based on the Michael addition/Schiff base reaction of polydopamine modified reduced graphene oxide was first proposed. Inspired by the mussel adhesion proteins, 3,4-dihydroxyphenylalanine (DA) was selected as a reducing agent to simultaneously reduce graphene oxide and self-polymerize to obtain the polydopamine-reduced graphene oxide (PDA-rGO). The PDA-rGO was then functionalized with thiols and amines by the reaction of thiol/amino groups with quinine groups of PDA-rGO via the Michael addition/Schiff base reaction. Several typical compounds containing thiol and/or amino groups such as 1-[(4-amino)phenylethynyl] ferrocene (Fc-NH2), cysteine (cys), and glucose oxidase (GOx) were selected as the model molecules to anchor on the surface of PDA-rGO using the strategy for construction of multifunctional electrochemical platforms. The experiments revealed that the composite grafted with ferrocene derivative shows excellent catalysis activity toward many electroactive molecules and could be used for individual or simultaneous detection of dopamine hydrochloride (DA) and uric acid (UA), or hydroquinone (HQ) and catechol (CC), while, after grafting of cysteine on PDA-rGO, simultaneous discrimination detection of Pb(2+) and Cd(2+) was realized on the composite modified electrode. In addition, direct electron transfer of GOx can be observed when GOx-PDA-rGO was immobilized on glassy carbon electrode (GCE). When glucose was added into the system, the modified electrode showed excellent electric current response toward glucose. These results inferred that the proposed multifunctional electrochemical platforms could be simply, conveniently, and effectively regulated through changing the anchored recognition or reaction groups. This study would provide a versatile method to design more detection or biosensing platforms through a chemical reaction strategy in the future.

Vertical nanowire arrays as a versatile platform for protein detection and analysis

Protein microarrays are valuable tools for protein assays. Reducing spot sizes from micro- to nano-scale facilitates miniaturization of platforms and consequently decreased material consumption, but faces inherent challenges in the reduction of fluorescent signals and compatibility with complex solutions. Here we show that vertical arrays of nanowires (NWs) can overcome several bottlenecks of using nanoarrays for extraction and analysis of proteins. The high aspect ratio of the NWs results in a large surface area available for protein immobilization and renders passivation of the surface between the NWs unnecessary. Fluorescence detection of proteins allows quantitative measurements and spatial resolution, enabling us to track individual NWs through several analytical steps, thereby allowing multiplexed detection of different proteins immobilized on different regions of the NW array. We use NW arrays for on-chip extraction, detection and functional analysis of proteins on a nano-scale platform that holds great promise for performing protein analysis on minute amounts of material. The demonstration made here on highly ordered arrays of indium arsenide (InAs) NWs is generic and can be extended to many high aspect ratio nanostructures.