Nanofabricated pores in 20 nm-thick silicon nitride membranes were used to probe various protein analytes as well as to perform an antigen-antibody binding assay. A two-compartment electrochemical cell was separated by a single nanopore, 28 nm in diameter. Adding proteins to one compartment caused current perturbations in the ion current flowing through the pore. These perturbations correlated with both the charge and the size of the protein or of a protein-protein complex. The potential of this nanotechnology for studying protein-protein interactions is highlighted with the sensitive detection of -human chorionic gonadotropin, a hormone and clinical biomarker of pregnancy, by monitoring in real time and at a molecular level the formation of a complex between hormones and antibodies in solution. In this form, the assay compared advantageously to immunoassays, with the important difference that labels, immobilization, or amplification steps were no longer needed. In conclusion, we present proof-of-principle that properties of proteins and their interactions can be investigated in solution using synthetic nanopores and that these interactions can be exploited to measure protein concentrations accurately.The development of more sensitive assays for proteins is highly desirable as it will have a major impact in proteomics (i.e., for the understanding of the role of proteins in complex processes) and in clinical diagnostics (i.e., for alternative test formats). Classic immunoassays, which are routinely used for protein detection, have a sensitivity that is significantly lower than deoxyribonucleic acid (DNA) assays based on an amplification by means of polymerase chain reaction (PCR).1 An elegant way to boost the sensitivity of protein assays is, hence, to use DNA as a label and employ DNA amplification, for example in immuno-PCR 2 or biobarcode assays, 3 which allow a significant decrease in the detection limits to a few tens of proteins.In parallel to these developments, the detection of single biological molecules has become accessible using ultrasensitive fluorescence microscopy, 4-6 which, together with scanning probe microscopy (SPM), 7 is able to reveal inter-and intramolecular interactions and structural information. 8,9 However, the above methods for protein analysis have inherent limitations, such as a requirement for labels, immobilization, or complicated instrumentation that may be overcome with nanoporesensing.10,11 Some unique advantages of using nanopores are (i) no labeling or immobilization of the analyte is necessary; (ii) the instrumental setup is simple and does not require any moving parts, and (iii) it allows real-time detection of the analyte. Nanopores are therefore well suited for studying proteins and interactions between proteins under native conditions and at the single molecule level.Using the biological pore R-hemolysin, Meller et al. could distinguish DNA analytes which only differ in sequence. 11However, biological pores have practical limitations due to operating pH, temperature, a...

We report the detection of protein molecules with nanofabricated pores using the resistive pulse sensing method. A 20-nm-thick silicon nitride membrane with a nanofabricated pore measuring about 55nm in diameter separated an electrolyte cell into two compartments. Current spike trains were observed when bovine serum albumin (BSA) was added to the negatively biased compartment. The magnitude of the spikes corresponded to particles 7–9nm in diameter (the size of a BSA molecule) passing through the pore. This suggests that the current spikes were current blockages caused by single BSA molecules. The presented nano-Coulter counting method could be applied to detect single protein molecules in free solution, and to study the translocation of proteins through a pore.

Efficient adhesion of gold thin films on dielectric or semiconductor substrates is essential in applications and research within plasmonics, metamaterials, 2D materials, and nanoelectronics. As a consequence of the relentless downscaling in nanoscience and technology, the thicknesses of adhesion layer and overlayer have reached tens of nanometers, and it is unclear if our current understanding is sufficient. In this report, we investigated how Cr and Ti adhesion layers influence the nanostructure of 2-20 nm thin Au films by means of high-resolution electron microscopy, complemented with atomic force microscopy and X-ray photoelectron spectroscopy. Pure Au films were compared to Ti/Au and Cr/Au bilayer systems. Both Ti and Cr had a striking impact on grain size and crystal orientation of the Au overlayer, which we interpret as the adhesion layer-enhanced wetting of Au and the formation of chemical bonds between the layers. Ti formed a uniform layer under the Au overlayer. Cr interdiffused with the Au layer forming a Cr-Au alloy. The crystal orientation of the Au layers was mainly [111] for all thin-film systems. The results showed that both adhesion layers were partially oxidized, and oxidation sources were scrutinized and found. A difference in bilayer electrical resistivity between Ti/Au and Cr/Au systems was measured and compared. On the basis of these results, a revised and more detailed adhesion layer model for both Ti/Au and Cr/Au systems was proposed. Finally, the implications of the results were analyzed, and recommendations for the selection of adhesion layers for nano-optics and nanoelectronics applications are presented.

We report the filling kinetics of different liquids in nanofabricated capillaries with rectangular cross-section by capillary force. Three sets of channels with different geometry were employed for the experiments. The smallest dimension of the channel cross-section was respectively 27, 50, and 73 nm. Ethanol, isopropanol, water and binary mixtures of ethanol and water spontaneously filled nanochannels with inner walls exposing silanol groups. For all the liquids the position of the moving liquid meniscus was observed to be proportional to the square root of time, which is in accordance with the classical Washburn kinetics. The velocity of the meniscus decreased both with the dimension of the channel and the ratio between the surface tension and the viscosity. In the case of water, air-bubbles were spontaneously trapped as channels were filled. For a binary mixture of 40% ethanol and water, no trapping of air was observed anymore. The filling rate was higher than expected, which also corresponds to the dynamic contact angle for the mixture being lower than that of pure ethanol. Nanochannels and porous materials share many physicochemical properties, e.g., the comparable pores size and extremely high surface to volume ratio. These similarities suggest that our nanochannels could be used as an idealized model to study mass transport mechanisms in systems where surface phenomena dominate.