Electrocatalytic Amplification of Single Nanoparticle Collisions Using DNA-Modified Surfaces

Abstract

Here we report on the effect of DNA modification on individual collisions between Pt nanoparticles (PtNPs) and ultramicroelectrode (UME) surfaces. These results extend recent reports of electrocatalytic amplification (ECA) arising from collisions between naked surfaces, and they are motivated by our interest in using ECA for low-level biosensing applications. In the present case, we studied collisions between naked PtNPs and DNA-modified Au and Hg UMEs and also collisions between DNA-modified PtNPs and naked Au and Hg UMEs. In all cases, the sensing reaction is the catalytic oxidation of N2H4. The presence of ssDNA (5-mer or 25-mer) immobilized on the UME surface has little effect on the magnitude or frequency of ECA signals, regardless of whether the electrode is Au or Hg. In contrast, when DNA is immobilized on the PtNPs and the electrodes are naked, clear trends emerge. Specifically, as the surface concentration of ssDNA on the PtNP surface increases, the magnitude and frequency of the current transients decrease. This trend is most apparent for the longer 25-mer. We interpret these results as follows. When ssDNA is immobilized at high concentration on the PtNPs, the surface sites on the NP required for electrocatalytic N2H4 oxidation are blocked. This leads to lower and fewer ECA signals. In contrast, naked PtNPs are able to transfer electrons to UMEs having sparse coatings of ssDNA.

Electrocatalytic amplification of DNA-modified nanoparticle collisions via enzymatic digestion

“…Consistent with an earlier report from our group, 2 these PtNP@ssDNA conjugates yield few collision signals (Scheme 1b), because DNA restricts access of N 2 H 4 to the electrocatalytic PtNP surface. After incubation of PtNP@ssDNA with 30 U of Exo I, however, about 50% of the collision activity (compared to naked PtNPs) returns (Scheme 1c).…”

“…2 To verify that this observation holds true even for the larger NPs used in the present study, we modified PtNPs using solutions containing the following ratios of PtNP : ssDNA—1 : 10, 1 : 25, 1 : 50, and 1 : 100, and then obtained ECA data using Au UMEs.…”

“…11 As discussed next, the experiment reported here is most similar to the latter approach. Finally, we note that the research groups of Unwin, 12,13 Zhang, 14,15 Koper, 12,16 Andreescu, 17 Alpuche-Aviles, 18 Crooks, 2,19–21 Stevenson, 22–24 and MacPherson 25 have all made important contributions to the general field of single-particle collision electrochemistry that have influenced the findings reported here.…”

“…Previous work from our lab has shown, however, that when DNA is present on colliding NPs, very little current results. 2 This is, of course, a consequence of DNA-induced blocking of catalytically active sites on the NP surface. This finding presents a clear problem for integration of ECA into biosensing schemes: specifically, if a biological recognition element is immobilized on the NPs, then little or no current will be observed upon impact.…”

Enzyme-free electrochemical immunosensor based on methylene blue and the electro-oxidation of hydrazine on Pt nanoparticles

“…While capable of rapid measurements, these sensors require complicated detection protocols or lack the sensitivity needed for detection in raw biological samples. Others have developed enzyme-free DNA sensors using methylene blue (MB) as a redox indicator and hydrazine as a substrate (Zhua et al 2006; Yu et al 2013; Aligrant et al 2015). However, these methods exhibit lower signal-to-background ratios and longer detection times compared with biosensors utilizing only hydrazine and Pt.…”