Synthetic nanopores have been used to study individual biomolecules in high thoroughput but their performance as sensors does not match biological ion channels. Controlling the translocation times of single-molecule analytes and their non-specific interaction with pore walls remain a challenge. Inspired by the olfactory sensilla of the insect antenna, here we show that coating nanopores with fluid bilayer lipids allows the pore diameters to be fine-tuned in sub-nanometre increments. Incorporation of mobile ligands in the lipid conferred specificity and slowed down the translocation of targeted proteins sufficiently to time-resolve translocation events of individual proteins. The lipid coatings also prevented pores from clogging, eliminated non-specific binding and enabled the translocation of amyloid-beta (Aβ) oligomers and fibrils. Through combined analysis of translocation time, volume, charge, shape and ligand affinity, different proteins were identified.

Biological protein pores and pore-forming peptides can generate a pathway for the flux of ions and other charged or polar molecules across cellular membranes. In nature, these nanopores have diverse and essential functions that range from maintaining cell homeostasis and participating in cell signaling to activating or killing cells. The combination of the nanoscale dimensions and sophisticated – often regulated – functionality of these biological pores make them particularly attractive for the growing field of nanobiotechnology. Applications range from single-molecule sensing to drug delivery and targeted killing of malignant cells. Potential future applications may include the use of nanopores for single strand DNA sequencing and for generating bio-inspired, and possibly, biocompatible visual detection systems and batteries. This article reviews the current state of applications of pore-forming peptides and proteins in nanomedicine, sensing, and nanoelectronics.

Bioinspired artificial water channels aim to combine the high permeability and selectivity of biological aquaporin (AQP) water channels with chemical stability. Here, we carefully characterized a class of artificial water channels, peptide-appended pillar [5]arenes (PAPs). The average single-channel osmotic water permeability for PAPs is 1.0(±0.3) × 10 −14 cm 3 /s or 3.5(±1.0) × 10 8 water molecules per s, which is in the range of AQPs (3.4∼40.3 × 10 8 water molecules per s) and their current synthetic analogs, carbon nanotubes (CNTs, 9.0 × 10 8 water molecules per s). This permeability is an order of magnitude higher than first-generation artificial water channels (20 to ∼10 7 water molecules per s). Furthermore, within lipid bilayers, PAP channels can self-assemble into 2D arrays. Relevant to permeable membrane design, the pore density of PAP channel arrays (∼2.6 × 10 5 pores per μm 2 ) is two orders of magnitude higher than that of CNT membranes (0.1∼2.5 × 10 3 pores per μm 2 ). PAP channels thus combine the advantages of biological channels and CNTs and improve upon them through their relatively simple synthesis, chemical stability, and propensity to form arrays.artificial aquaporins | artificial water channels | peptide-appended pillar [5]arene | single-channel water permeability | two-dimensional arrays T he discovery of the high water and gas permeability of aquaporins (AQPs) and the development of artificial analogs, carbon nanotubes (CNTs), have led to an explosion in studies aimed at incorporating such channels into materials and devices for applications that use their unique transport properties (1-9). Areas of application include liquid and gas separations (10-13), drug delivery and screening (14), DNA recognition (15), and sensors (16). CNTs are promising channels because they conduct water and gas three to four orders of magnitude faster than predicted by conventional Hagen-Poiseuille flow theory (11). However, their use in large-scale applications has been hampered by difficulties in producing CNTs with subnanometer pore diameters and fabricating membranes in which the CNTs are vertically aligned (4). AQPs also efficiently conduct water across membranes (∼3 billion molecules per second) (17) and are therefore being studied intensively for their use in biomimetic membranes for water purification and other applications (1, 2, 18). The largescale applications of AQPs is complicated by the high cost of membrane protein production, their low stability, and challenges in membrane fabrication (1).Artificial water channels, bioinspired analogs of AQPs created using synthetic chemistry (19), ideally have a structure that forms a water-permeable channel in the center and an outer surface that is compatible with a lipid membrane environment (1). Interest in artificial water channels has grown in recent years, following decades of research and focus on synthetic ion channels (19). However, two fundamental questions remain: (i) Can artificial channels approach the permeability and selectivity of AQP water chan...

No abstract

Herein we describe a rapid, reproducible, and straightforward method to form copies of functional membrane arrays with various lipid compositions and the application of these arrays for the screening of drug-membrane and protein-membrane interactions. We employed topographically patterned agarose gels to stamp spatially addressable arrays of supported bilayers on glass and confirmed the fluidity of these membranes by fluorescence recovery experiments. We took advantage of the storage capability of hydrogels and demonstrated that inking posts on an agarose stamp, with extremely small volumes ( 1 mL) of a solution that contains liposomes, was sufficient to transfer at least 100 copies of a membrane array without the need for reinking. We used stamped membrane arrays for screening the interactions of a protein (annexin V) and an anti-inflammatory drug (nimesulide) with bilayers of various lipid compositions and discovered that the interaction of the prescription drug nimesulide with membranes depends on the membrane cholesterol content.Interest in supported bilayers [1][2][3] includes studies of the dynamic structure of membranes, [4,5] their self-assembly, [5] lipid-protein interactions, [5] ligand-receptor interactions, [5][6][7][8] development of membrane-based biosensors, [5,[9][10][11][12][13][14][15] and drug discovery.[16] Furthermore, many pharmaceuticals are known to interact with biological membranes and, as such, assays for testing drug-membrane interactions are important for a better understanding of drug activity, targeting, and toxicity.[17] To use supported bilayers efficiently for the study of the aforementioned processes, the membranes must be fluid [1,16,18,19] and mechanically stable. [19] Techniques that are currently employed to form arrays of supported membranes exploit a) the deposition of droplets of a liposome solution onto surfaces, [6,18] b) vesicle fusion from a bulk solution onto patterned substrates, [20,21] c) delivery of liposomes by microfluidic channels, [22,23] and d) microcontact printing with poly-(dimethylsiloxane) (PDMS). [24] An ideal fabrication method for the application of membrane arrays for screening protein-membrane or drugmembrane interactions would consist of the rapid creation of many functional copies of an array of different bilayers with minimal consumption of the amount of lipid. Among the existing methods, microcontact printing allows the creation of many spots of membranes in parallel. To prepare arrays with various compositions, however, posts of the stamp used for microcontact printing must be inked individually. Such an inking procedure can be time consuming and can introduce heterogeneity into the stamped arrays. It would therefore be advantageous if a biocompatible stamp, once inked, could store the inking solution and allow multiple transfers without the need for reinking.Herein, we demonstrate that stamping with hydrogel stamps allows multiple stamping while using minute amounts of material. We fabricated stamps from agarose gel (4 %) with a pore size suf...