Plasmonic resonances in metallic nanoparticles have been used since antiquity to colour glasses. The use of metal nanostructures for surface colourization has attracted considerable interest following recent developments in plasmonics. However, current top-down colourization methods are not ideally suited to large-scale industrial applications. Here we use a bottom-up approach where picosecond laser pulses can produce a full palette of non-iridescent colours on silver, gold, copper and aluminium. We demonstrate the process on silver coins weighing up to 5 kg and bearing large topographic variations (∼1.5 cm). We find that colours are related to a single parameter, the total accumulated fluence, making the process suitable for high-throughput industrial applications. Statistical image analyses of laser-irradiated surfaces reveal various nanoparticle size distributions. Large-scale finite-difference time-domain computations based on these nanoparticle distributions reproduce trends seen in reflectance measurements, and demonstrate the key role of plasmonic resonances in colour formation.

Nanopore fabrication by controlled breakdown (CBD) overcomes many of the challenges of traditional nanofabrication techniques, by reliably forming solid-state nanopores sub-2 nm in size in a low-cost and scalable way for nucleic acid analysis applications. Herein, the breakdown kinetics of thin dielectric membranes immersed in a liquid environment are investigated in order to gain deeper insights into the mechanism of solid-state nanopore formation by high electric fields. For various fabrication conditions, we demonstrate that nanopore fabrication time is Weibull-distributed, in support of the hypothesis that the fabrication mechanism is a stochastic process governed by the probability of forming a connected path across the membrane (i.e. a weakest-link problem). Additionally, we explore the roles that various ions and solvents play in breakdown kinetics, revealing that asymmetric pH conditions across the membrane can significantly affect nanopore fabrication time for a given voltage polarity. These results, characterizing the stochasticity of the nanopore fabrication process and highlighting the parameters affecting it, should assist researchers interested in exploiting the potential of CBD for nanofluidic channel fabrication, while also offering guidance towards the conceivable manufacturing of solid-state nanopore-based technologies for DNA sequencing applications.

Using a solid-state nanopore to measure the concentration of clinically relevant target analytes, such as proteins or specific DNA sequences, is a major goal of nanopore research. This is usually achieved by measuring the capture rate of the target analyte through the pore. However, progress is hindered by sources of systematic error that are beyond the level of control currently achievable with state-of-the-art nanofabrication techniques. In this work, we show that the capture rate process of solid-state nanopores is subject to significant sources of variability, both within individual nanopores over time and between different nanopores of nominally identical size, which are absent from theoretical electrophoretic capture models. We experimentally reveal that these fluctuations are inherent to the nanopore itself and make nanopore-based molecular concentration determination insufficiently precise to meet the standards of most applications. In this work, we present a simple method by which to reduce this variability, increasing the reliability, accuracy, and precision of single-molecule nanopore-based concentration measurements. We demonstrate controlled counting, a concentration measurement technique, which involves measuring the simultaneous capture rates of a mixture of both the target molecule and an internal calibrator of precisely known concentration. Using this method on linear DNA fragments, we show empirically that the requirements for precisely controlling the nanopore properties, including its size, height, geometry, and surface charge density or distribution, are removed while allowing for higher-precision measurements. The quantitative tools presented herein will greatly improve the utility of solid-state nanopores as sensors of target biomolecule concentration.

Single-molecule counting is the most accurate and precise method for determining the concentration of a biomarker in solution and is leading to the emergence of digital diagnostic platforms enabling precision medicine. In principle, solid-state nanopores—fully electronic sensors with single-molecule sensitivity—are well suited to the task. Here we present a digital immunoassay scheme capable of reliably quantifying the concentration of a target protein in complex biofluids that overcomes specificity, sensitivity, and consistency challenges associated with the use of solid-state nanopores for protein sensing. This is achieved by employing easily-identifiable DNA nanostructures as proxies for the presence (“1”) or absence (“0”) of the target protein captured via a magnetic bead-based sandwich immunoassay. As a proof-of-concept, we demonstrate quantification of the concentration of thyroid-stimulating hormone from human serum samples down to the high femtomolar range. Further optimization to the method will push sensitivity and dynamic range, allowing for development of precision diagnostic tools compatible with point-of-care format.

The androgen receptor (AR) in Sertoli cells mediates the actions of testosterone on spermatogenesis. However, the transcription factors responsible for AR gene regulation in Sertoli cells remain unknown. In this study, we determined that nuclear factor-kappaB (NF-kappaB) regulates transcription of AR in primary cultures of Sertoli cells isolated from testes of adult rats. Electrophoretic mobility shift and antibody supershift assays with nuclear extracts prepared from Sertoli cells identified two binding sites, termed kappaB1 at -491/-482 bp and kappaB2 at -574/-565 bp, upstream of the transcription start site of the AR gene that bind the NF-kappaB subunits, p50 and p65. DNAse I footprint analyses showed that binding of the p50 NF-kappaB subunit protected the same regions on the rat AR promoter. Analyses of AR promoter-luciferase reporter gene activity after transfection of primary cultures of Sertoli cells demonstrated that mutation of the kappaB2 site or combined mutation of the kappaB1 and kappaB2 sites reduced activity by 40%. Preferential binding of the transcriptionally active p65/p50 heterodimer to the kappaB2 site rather than to the kappaB1 site supported these observations. Overexpression of the NF-kappaB p65 and p50 subunits in Sertoli cells increased activity from the wild-type AR promoter and the promoter with mutation of the kappaB1 site, but not the kappaB2 site. Activity was further stimulated by CBP (CREB binding protein), a coactivator of p65 transcriptional activity. Taken together, our data show that NF-kappaB is an activator of AR gene transcription in Sertoli cells and may be an important determinant of androgen activity during spermatogenesis.