Established methods for characterizing proteins typically require physical or chemical modification steps or cannot be used to examine individual molecules in solution. Ionic current measurements through electrolyte-filled nanopores can characterize single native proteins in an aqueous environment, but currently offer only limited capabilities. Here we show that the zeptolitre sensing volume of bilayer-coated solid-state nanopores can be used to determine the approximate shape, volume, charge, rotational diffusion coefficient and dipole moment of individual proteins. To do this, we developed a theory for the quantitative understanding of modulations in ionic current that arise from the rotational dynamics of single proteins as they move through the electric field inside the nanopore. The approach allows us to measure the five parameters simultaneously, and we show that they can be used to identify, characterize and quantify proteins and protein complexes with potential implications for structural biology, proteomics, biomarker detection and routine protein analysis.

The lateral flow test has become the standard bioassay format in low-resource settings because it is rapid, easy to use, low in cost, uses reagents stored in dry form, and is equipment-free. However, lateral flow tests are often limited to a single chemical delivery step and not capable of the multi-step processing characteristic of high performance laboratory-based assays. To address this limitation, we are developing a paper network platform that extends the conventional lateral flow test to two dimensions; this allows incorporation of multi-step chemical processing, while still retaining the advantages of conventional lateral flow tests. Here we demonstrate this format for an easy-to-use, signal-amplified sandwich format immunoassay for the malaria protein PfHRP2. The card contains reagents stored in dry form such that the user need only add sample and water. The multiple flows in the device are activated in a single user step of folding the card closed; the configuration of the paper network automatically delivers the appropriate volumes of i) sample plus antibody conjugated to a gold particle label, ii) a rinse buffer, and iii) a signal amplification reagent to the capture region. These results highlight the potential of the paper network platform to enhance access to high-quality diagnostic capabilities in low-resource settings in the developed and developing worlds.

This paper demonstrates that high-bandwidth current recordings in combination with low-noise silicon nitride nanopores make it possible to determine the molecular volume, approximate shape, and dipole moment of single native proteins in solution without the need for labeling, tethering, or other chemical modifications of these proteins. The analysis is based on current modulations caused by the translation and rotation of single proteins through a uniform electric field inside of a nanopore. We applied this technique to nine proteins and show that the measured protein parameters agree well with reference values but only if the nanopore walls were coated with a nonstick fluid lipid bilayer. One potential challenge with this approach is that an untethered protein is able to diffuse laterally while transiting a nanopore, which generates increasingly asymmetric disruptions in the electric field as it approaches the nanopore walls. These "off-axis" effects add an additional noise-like element to the electrical recordings, which can be exacerbated by nonspecific interactions with pore walls that are not coated by a fluid lipid bilayer. We performed finite element simulations to quantify the influence of these effects on subsequent analyses. Examining the size, approximate shape, and dipole moment of unperturbed, native proteins in aqueous solution on a single-molecule level in real time while they translocate through a nanopore may enable applications such as identifying or characterizing proteins in a mixture, or monitoring the assembly or disassembly of transient protein complexes based on their shape, volume, or dipole moment.

Point-of-care diagnostic assays that are rapid, easy-to-use, and low-cost are needed for use in low-resource settings; the lateral flow test has become the standard bioassay format in such settings because it meets those criteria. However, for a number of analytes, conventional lateral flow tests lack the sensitivity needed to have clinical utility. To address this limitation, we are developing a paper network platform that extends the conventional lateral flow test to two dimensions. The two-dimensional structures allow incorporation of multi-step processes for improved sensitivity, while still retaining the positive aspects of conventional lateral flow tests. Here we create an easy-to-use, signal-amplified immunoassay based on a modified commercial strip test for human chorionic gonadotropin, the hormone used to detect pregnancy, and demonstrate an improved limit of detection compared to a conventional lateral flow assay. These results highlight the potential of the paper network platform to enhance access to high-quality diagnostic capabilities in low-resource settings in the developed and developing worlds.

The functional analysis of single ion channel proteins presents a serious bottleneck in the process of finding new pharmacologically active compounds. Single channel recording methods currently available (patch clamp, [1] black lipid membrane (BLM) [2] ) are not suited for automation and miniaturization. However, new techniques such as combinatorial chemistry [3] and combinatorial genetics, [4] which pro-

Nanopores with diameters from 20 to 50 nm in silicon nitride (SiN x ) windows are useful for singlemolecule studies of globular macromolecules. While controlled breakdown (CBD) is gaining popularity as a method for fabricating nanopores with reproducible size control and broad accessibility, attempts to fabricate large nanopores with diameters exceeding ∼20 nm via breakdown often result in undesirable formation of multiple nanopores in SiN x membranes. To reduce the probability of producing multiple pores, we combined two strategies: laser-assisted breakdown and controlled pore enlargement by limiting the applied voltage. Based on laser power-dependent increases in nanopore conductance upon illumination and on the absence of an effect of ionic strength on the ratio between the nanopore conductance before and after laser illumination, we suggest that the increased rate of controlled breakdown results from laser-induced heating. Moreover, we demonstrate that conductance values before and after coating the nanopores with a fluid lipid bilayer can indicate fabrication of a single nanopore versus multiple nanopores. Complementary flux measurements of Ca 2+ through the nanopore typically confirmed assessments of single or multiple nanopores that we obtained using the coating method. Finally, we show that thermal annealing of CBD pores significantly increased the success rate of coating and reduced the current noise before and after lipid coating. We characterize the geometry of these nanopores by analyzing individual resistive pulses produced by translocations of spherical proteins and demonstrate the usefulness of these nanopores for estimating the approximate molecular shape of IgG proteins.

Over the course of their wildly successful proliferation across the earth, the insects as a taxon have evolved enviable adaptations to their diverse habitats, which include adhesives, locomotor systems, hydrophobic surfaces, and sensors and actuators that transduce mechanical, acoustic, optical, thermal, and chemical signals. Insect‐inspired designs currently appear in a range of contexts, including antireflective coatings, optical displays, and computing algorithms. However, as over one million distinct and highly specialized species of insects have colonized nearly all habitable regions on the planet, they still provide a largely untapped pool of unique problem‐solving strategies. With the intent of providing materials scientists and engineers with a muse for the next generation of bioinspired materials, here, a selection of some of the most spectacular adaptations that insects have evolved is assembled and organized by function. The insects presented display dazzling optical properties as a result of natural photonic crystals, precise hierarchical patterns that span length scales from nanometers to millimeters, and formidable defense mechanisms that deploy an arsenal of chemical weaponry. Successful mimicry of these adaptations may facilitate technological solutions to as wide a range of problems as they solve in the insects that originated them.

This paper presents a method for monitoring chemical reactions on individual molecules. We exploit the functional properties of an ion-channel-forming peptide to follow the conversion of chemical groups on molecules attached near the opening of these semisynthetic nanopores. It is known that the conductance properties of derivatives of gramicidin A (gA) can be measurably different.[1] Here, we take advantage of singlechannel conductance measurements to monitor in situ the multistep conversion of a tert-butyloxycarbonyl-protected (Boc-protected) amine to the free amine and the subsequent diazotization/hydrodediazoniation of the amine to an alcohol functionality on molecules attached to gA. These model reactions show that gA provides a simple nanoscale platform for sensing external chemical reagents with high sensitivity and selectivity.Gramicidin A is a natural ion-channel-forming peptide (molecular weight 1.9 kDa, secreted from the bacterium Bacillus brevis) that incorporates into lipid bilayers and facilitates the transmembrane flux of monovalent cations upon reversible dimerization in bilayers (Figure 1 A).[2] Although several artificial ion channels based on genetically engineered proteins, [3] peptides, [4] or oligomers of organic molecules [5] have been explored for their potential use as chemo-and biosensors, [6] most of these sensors are designed to sense particular structural properties of chemical or biochemical species (such as the ability of a ligand to interact with a binding pocket). In this work, we explore the use of ion channels derived from gA to detect chemicals that display particular functional properties (such as the ability to facilitate specific chemical transformations). Bayley and co-workers have previously demonstrated that wild-type and genetically modified a-hemolysin (a 232.4 kDa protein [7] ) can be used to monitor the conversion of a light-driven reaction by recording distinct conductances of intermediates throughout the course of the reaction.[3c] Here, we demonstrate that it is possible to monitor the synthetic conversion of reactive chemical groups on molecules attached to gA in the presence of external chemical reagents in solution to afford identifiable and isolatable products with measurably different single-channel conductance. This research extends the pioneering work on a-hemolysin to a synthetically accessible platform-gA-that is readily available in high purity and in useful quantities.We synthesized and characterized derivatives of gA carrying N-Boc-protected glycine (1), glycine (2), and glycolic acid (3) moieties attached to the C terminus of commercially available gA (Figure 1 B). The Supporting Information summarizes the details of the syntheses. We measured the single-channel current of 1-3 by incorporating them into planar lipid bilayers. Figure 1 C shows representative current-versus-time traces of 1-3 under an applied potential of 100 mV in buffered solution (1 M KCl, 0.01 M HEPES buffer, pH 7.4). These traces show that the conductance of ions through deriva...