Attoampere Nanoelectrochemistry

Abstract

to batteries. [6] Additionally, it allows us to increase our understanding of molecular interactions in liquid, which is currently based on theoretical models of ensemble measurements. Towards these goals, scanning electrochemical microscopy (SECM), including the use of nanopipettes, [7][8][9] has been developed to sense electrochemical reactions locally, providing spatial resolution of typically μm to the sub-μm range, [10][11][12] but also fast reactions on nanometric particles could be resolved when well isolated. [13,14] SECM techniques are now well-established for probing electrochemical systems at the micro-and nanoscale levels. [15,16] Scanning probes have exploited redox-cycling amplification to reduce the electrode dimensions while keeping a reasonable signal level. [11,17,18] Electrochemical scanning tunneling microscopy (EC-STM) has been used to study electrochemistry indirectly from a molecular electronics perspective. [19,20] To date, these techniques have enabled measurements down to the fA (10 −15 Ampere) range, [11,[21][22][23][24][25] which is still not sensitive enough to obtain electrochemical signals at the nanoscale, except in the specific case of redox cycling amplification when ferrocene (Fc) is confined between 2 neighboring electrodes at the nanoscale. [23,25] For the versatile measurement of electrochemical currents at the nanoscale aA (10 −18 Ampere) sensitivity is crucial.Electrochemical microscopy techniques have extended the understanding of surface chemistry to the micrometer and even sub-micrometer level. However, fundamental questions related to charge transport at the solidelectrolyte interface, such as catalytic reactions or operation of individual ion channels, require improved spatial resolutions down to the nanoscale. A prerequisite for single-molecule electrochemical sensitivity is the reliable detection of a few electrons per second, that is, currents in the atto-Ampere (10 −18 A) range, 1000 times below today's electrochemical microscopes. This work reports local cyclic voltammetry (CV) measurements at the solid-liquid interface on ferrocene self-assembled monolayer (SAM) with sub-atto-Ampere sensitivity and simultaneous spatial resolution < 80 nm. Such sensitivity is obtained through measurements of the charging of the local faradaic interface capacitance at GHz frequencies. Nanometer-scale details of different molecular organizations with a 19% packing density difference are resolved, with an extremely small dispersion of the molecular electrical properties. This is predicted previously based on weak electrostatic interactions between neighboring redox molecules in a SAM configuration. These results open new perspectives for nano-electrochemistry like the study of quantum mechanical resonance in complex molecules and a wide range of applications from electrochemical catalysis to biophysics.

Redox-labelled electrochemical aptasensors with nanosupported cancer cells

“…The absolute I peak value is expected to be in the tens of pico-Amperes for a single cell, which could be measured with commercial equipment. Interestingly, the recent breakthrough in electrochemistry instrumentation allowing CVs at the atto-Ampere level for redox-labelled molecules would be directly beneficial to the present sensing approach, granting subcellular studies with nanoelectrodes in the 10-nm range (Grall et al, 2021). Finally, this nano-supported cell approach could also be beneficial to nanowire based aptasensors (Kutovyi et al, 2020) for subcellular sensing.…”

Nanoscale electrochemical charge transfer kinetics investigated by electrochemical scanning microwave microscopy

“…While this resolution is difficult to achieve with other techniques, the sensitivity is insufficient to measure current at the nanoscale. However, as we have shown previously, it is possible to go beyond this limitation and achieve aA (10 −18 A) 25 sensitivity by using a GHz heterodyne impedance sensing method combined with the EC-STM. This was technically realized by integrating a vector network analyzer (VNA) into EC-STM.…”

“…This was technically realized by integrating a vector network analyzer (VNA) into EC-STM. 25 We will refer to this new type of microscopy as Electrochemical Scanning Microwave Microscope (EC-SMM). The developed heterodyne impedance sensing methods have significant advantages compared to other methods in sensitivity (down to aA) and specificity (differential impedance is sensed) but also wide frequency bandwidth.…”

Application of Near-Field Scanning Microwave Microscopy in Liquid Environment

“…The phenomenon including microscopic phase separation and metal-insulator phase transitions about phase-change materials [14,15] is also observed by NSMM. Since microwave detection has a relatively higher sensitivity and the properties of non-destructive detection, it is appealing to the field of electrochemistry [16][17][18], biological [19][20][21], food industries, and medical industries [22,23]. Especially in the study of medical imaging, it has attracted great interest during the past twenty years, since it has a significant capacity for the detecting abnormal tissue of the human body like malignant tissue, and the frequencies range of the electromagnetic is around 500 MHz to 10 GHz [24][25][26][27][28].…”