Herein the problem of colloidal instability on electrochemically detected nanoparticle (NP) collisions with a Hg ultramicroelectrode (UME) by electrocatalytic amplification is addressed. NP tracking analysis (NTA) shows that rapid aggregation occurs in solution after diluting citrate-stabilized Pt NPs with hydrazine/phosphate buffers of net ionic strength greater than 70 mM. Colloidal stability improves by lowering the ionic strength, indicating that aggregation processes were strongly affected by charge screening of the NP double layer interactions at high cation concentrations. For the system of lowest ionic strength, the overwhelming majority of observed electrocatalytic current signals represent single NP/electrode impacts, as confirmed by NTA kinetic monitoring. NP diffusion coefficients determined by NTA and NP impact electroanalysis are in excellent agreement for the stable colloids, which signifies that the sticking probability of Pt NPs interacting with Hg is unity and that the observed NP impact rate agrees with the expected steady-state diffusive flux expression for the spherical cap Hg UME.

Here we report a sensing scheme for detection of microRNA (miRNA) using electrocatalytic amplification (ECA). ECA is a method in which nanoparticles (NPs) that are catalytic for a specific electrochemical reaction collide with an inert electrode surface. Each collision results in a detectable current transient. In the present article, we show that this general approach can be extended to detection of miRNA. Specifically, PtNPs are modified with a single-strand DNA (ssDNA) shell that is complementary to the miRNA target. Next, the ssDNA:miRNA conjugate is formed, which passivates the PtNP surface. In the presence of an enzyme called duplex specific nuclease (DSN), however, a fraction of the surface-bound DNA is removed thereby exposing some of the PtNP surface. In other words, the electrocatalytic properties of the PtNPs are reactivated only if miRNA complementary to ssDNA is present. This methodology resolves a number of problems that have rendered ECA ineffective for biosensing applications. Moreover, the results suggest that the underlying chemistry is broadly applicable to nucleic acid sensing.

An integrated microfluidic/magnetophoretic methodology was developed for improving signal response time and detection limits for the chronoamperometric observation of discrete nanoparticle/electrode interactions by electrocatalytic amplification. The strategy relied on Pt-decorated iron oxide nanoparticles which exhibit both superparamagnetism and electrocatalytic activity for the oxidation of hydrazine. A wet chemical synthetic approach succeeded in the controlled growth of Pt on the surface of FeO/Fe3O4 core/shell nanocubes, resulting in highly uniform Pt-decorated iron oxide hybrid nanoparticles with good dispersibility in water. The unique mechanism of hybrid nanoparticle formation was investigated by electron microscopy and spectroscopic analysis of isolated nanoparticle intermediates and final products. Discrete hybrid nanoparticle collision events were detected in the presence of hydrazine, an electrochemical indicator probe, using a gold microband electrode integrated into a microfluidic channel. In contrast with related systems, the experimental nanoparticle/electrode collision rate correlates more closely with simple theoretical approximations, primarily due to the accuracy of the nanoparticle tracking analysis method used to quantify nanoparticle concentrations and diffusion coefficients. Further modification of the microfluidic device was made by applying a tightly focused magnetic field to the detection volume to attract the magnetic nanoprobes to the microband working electrode, thereby resulting in a 6-fold increase to the relative frequency of chronoamperometric signals corresponding to discrete nanoparticle impact events.

We report electrochemical catalytic amplification of individual collisions between ∼57 nm diameter Pt nanoparticles (Pt NPs) and 12.5 μm diameter Au ultramicroelectrodes modified with passivating, electrostatically assembled polyelectrolyte multilayer (PEM) films prepared by the layer-by-layer deposition method. Two key findings are reported. First, despite the thicknesses of the insulating PEM films, which range up to 5 nm, electrons are able to tunnel from the Pt NPs to the electrode resulting in electrocatalytic N2H4 oxidation at the PEM film-solution interface. These single-particle measurements are in accord with prior reports showing that the electrochemical activity of passive PEM films can be reactivated by adsorption of metallic NPs. Second, it is possible to control the frequency of the collisions by manipulating the net electrostatic charge present on the outer surface of the PEM thin film. These results, which demonstrate that chemistry can be used to control electrocatalytic amplification, set the stage for future sensing applications.

Np collisions electrochemically detected post-Exo I digestion.

One of the most challenging fundamental problems in establishing prebiotically plausible routes for phosphorylation reactions using phosphate is that they are thermodynamically unfavorable in aqueous conditions. Diamidophosphate (DAP), a potentially prebiotically relevant compound, was shown to phosphorylate nucleosides in aqueous medium, albeit at a very slow rate (days/weeks). Here, we demonstrate that performing these reactions within an aerosol environment, a suitable model for the early Earth ocean-air interface, yields higher reaction rates when compared to bulk solution, thus overcoming these rate limitations. As a proof-of-concept, we demonstrate the effective conversion (~6.5–10%) of uridine to uridine-2′,3′-cyclophosphate in less than 1 h. These results suggest that aerosol environments are a possible scenario in which prebiotic phosphorylation could have occurred despite unfavorable rates in bulk solution.

Organophosphates were likely an important class of prebiotic molecules.However,their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals,i sw idely viewed as am ajor barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea-based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a"warm little pond" scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes,urea, ammonium formate,and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allowustopropose aholistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals,a llowing significant organic phosphorylation under plausible prebiotic conditions. Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

Organophosphates were likely an important class of prebiotic molecules. However, their presence on the early Earth is strongly debated because the low availability of phosphate, which is generally assumed to have been sequestered in insoluble calcium and iron minerals, is widely viewed as a major barrier to organophosphate generation. Herein, we demonstrate that cyanide (an essential prebiotic precursor) and urea‐based solvents could promote nucleoside phosphorylation by transforming insoluble phosphate minerals in a “warm little pond” scenario into more soluble and reactive species. Our results suggest that cyanide and its derivatives (metal cyanide complexes, urea, ammonium formate, and formamide) were key reagents for the participation of phosphorus in chemical evolution. These results allow us to propose a holistic scenario in which an evaporitic environment could concentrate abiotically formed organics and transform the underlying minerals, allowing significant organic phosphorylation under plausible prebiotic conditions.