The use of nanocarriers within resistive pulse sensing facilitates the detection and quantification of analytes. To date the field has been dominated by polyionic carriers or nanomaterials. Together they combine the recognition elements of a ligand with a stable support, facilitating the sample handling, analysis times, and multiplex detection. Here we develop the use of peptide-functionalized superparamagnetic nanocarriers to extract and quantify metal ions in solution. The interaction between nickel and the peptide ligand is measured as a change in translocation velocity of the carrier. The magnitude of change is proportional to the concentration of the metal ions in solution. Unlike DNA aptamers where a change in the tertiary structure and the folding of the polyanionic backbone influences the carrier velocity, the peptides here had a lower net charge under the assay conditions. To try and enhance the signal we engineered charged groups within the peptide to explore the effects on the signal. In all cases the metal ion binding dominated the velocity of the carrier. The assay was shown to work across 3 orders of magnitude and can detect Ni 2+ in the presence of some other heavy metal ions. We demonstrate this by quantifying Ni 2+ in both tap and pond water. The work allows for future multiplexed sensing strategies using both peptides and DNA aptamers in resistive pulse sensors.

The pollution of heavy metal ions within the environmental is a global problem. The rapid and precise removal of these contaminants can be aided by identifying and quantifying the composition of the sample. It is therefore crucial to develop effective portable analytical techniques to determine the levels of heavy metal contamination.Paper-based analytical devices (PADs) offer a low-cost method making them an excellent platform for onsite environmental sensors. Here we demonstrate how a PAD can be integrated into a multi-use Nanopore platform. The PAD was functionalised with different recognition ligands, who's surface charge densities varied in the presence of an analyte. The surface of the PAD was placed in contact with a Nanopore which exhibited Ion Current Rectification (ICR). The extent of ICR, was dependent upon the PAD's surface charge, and the presence of the analyte of interest i.e. the ICR phenomena was exaggerated or diminished indicating the presence of the metal ion in solution.We demonstrate the potential of PAD-ICR using a PAD functionalised with a peptide aptamer specific for nickel ions. Allowing the detection of nickel(II) as low as 0.25 μM even in the presence of other metal ions. After any measurement, the Nanopore surface can be wiped clean, and reused. PAD-ICR can also be adapted as a multiplexed sensor. This is demonstrated using a PAD with three different DNA aptamers for simultaneous and specific detection of nickel, mercury, and lead ions.

DNAzymes are DNA oligonucleotides that can undergo a specific chemical reaction in the presence of a cofactor. Ribonucleases are a specific form of DNAzymes where a tertiary structure undergoes cleavage at a single ribonuclease site. The cleavage is highly specificity to co-factors, which makes them excellent sensor recognition elements. Monitoring the change in structure upon cleavage has given rise to many sensing strategies; here we present a simple and rapid method of following the reaction using resistive pulse sensors, RPS. To demonstrate this methodology, we present a sensor for Ca2+ ions in solution. A nanoparticle was functionalised with a Ca2+ DNAzyme, and it was possible to follow the cleavage and rearrangement of the DNA as the particles translocate the RPS. The binding of Ca2+ caused a conformation change in the DNAzyme, which was monitored as a change in translocation speed. A 30 min assay produced a linear response for Ca2+ between 1–9 μm, and extending the incubation time to 60 min allowed for a concentration as low as 0.3 μm. We demonstrate that the signal is specific to Ca2+ in the presence of other metal ions, and we can quantify Ca2+ in tap and pond water samples.

The pollution of heavy metal ions within the environmental is a global problem. The rapid and precise removal of these contaminants can be aided by identifying and quantifying the composition of the sample. It is therefore crucial to develop effective portable analytical techniques to determine the levels of heavy metal contamination. Paper-based analytical devices (PADs) offer a low cost method making them an excellent platform for onsite environmental sensors. Here we demonstrate how a PAD can be integrated into a multi-use Nanopore platform. The PAD was functionalised with different recognition ligands, who’s surface charge densities varied in the presence of an analyte. The surface of the PAD was placed in contact with a Nanopore which exhibited Ion Current Rectification (ICR). The extent of ICR, was dependent upon the PAD’s surface charge, and the presence of the analyte of interest i.e. the ICR phenomena was exaggerated or diminished indicating the presence of the metal ion in solution. We demonstrate the potential of PAD-ICR using a PAD functionalised with a peptide aptamer specific for nickel ions. Allowing the detection of nickel(II) as low as 0.25 μM even in the presence of other metal ions. After any measurement, the Nanopore surface can be wiped clean, and reused.

The pollution of heavy metal ions within the environmental is a global problem. The rapid and precise removal of these contaminants can be aided by identifying and quantifying the composition of the sample. It is therefore crucial to develop effective portable analytical techniques to determine the levels of heavy metal contamination. Paper-based analytical devices (PADs) offer a low cost method making them an excellent platform for onsite environmental sensors. Here we demonstrate how a PAD can be integrated into a multi-use Nanopore platform. The PAD was functionalised with different recognition ligands, who’s surface charge densities varied in the presence of an analyte. The surface of the PAD was placed in contact with a Nanopore which exhibited Ion Current Rectification (ICR). The extent of ICR, was dependent upon the PAD’s surface charge, and the presence of the analyte of interest i.e. the ICR phenomena was exaggerated or diminished indicating the presence of the metal ion in solution. We demonstrate the potential of PAD-ICR using a PAD functionalised with a peptide aptamer specific for nickel ions. Allowing the detection of nickel(II) as low as 0.25 μM even in the presence of other metal ions. After any measurement, the Nanopore surface can be wiped clean, and reused.