Topographic, Electrochemical, and Optical Images Captured Using Standing Approach Mode Scanning Electrochemical/Optical Microscopy

Abstract

We developed a high-resolution scanning electrochemical microscope (SECM) for the characterization of various biological materials. Electrode probes were fabricated by Ti/Pt sputtering followed by parylene C-vapor deposition polymerization on the pulled optical fiber or glass capillary. The effective electrode radius estimated from the cyclic voltammogram of ferrocyanide was found to be 35 nm. The optical aperture size was less than 170 nm, which was confirmed from the cross section of the near-field scanning optical microscope (NSOM) image of the quantum dot (QD) particles with diameters in the range of 10-15 nm. The feedback mechanism controlling the probe-sample distance was improved by vertically moving the probe by 0.1-3 microm to reduce the damage to the samples. This feedback mode, defined as "standing approach (STA) mode" (Yamada, H.; Fukumoto, H.; Yokoyama, T.; Koike, T. Anal. Chem. 2005, 77, 1785-1790), has allowed the simultaneous electrochemical and topographic imaging of the axons and cell body of a single PC12 cell under physiological conditions for the first time. STA-mode feedback imaging functions better than tip-sample regulation by the conventionally available AFM. For example, polystyrene beads (diameter approximately 6 microm) was imaged using the STA-mode SECM, whereas imaging was not possible using a conventional AFM instrument.

Development of High-Resolution Scanning Electrochemical Microscopy for Nanoscale Topography and Electrochemical Simultaneous Imaging

“…Specifically, topography-related artifacts in these images can be avoided by employing probe-sample distance control. Various feedback distance control systems have been developed, including those based on atomic force microscopy, 15,16 shear force, [17][18][19] impedance, [20][21][22] faradaic current, 20,23 ion current, 11,12,24 and electrochemical signals. [25][26][27] Impedance-feedback and constantcurrent distance control systems are effective because additional modification of the probe for distance control is not required.…”

“…17 Therefore, we developed a tuning-fork-based distance control SECM and successfully imaged the topography respiration activity of a single cell. 18 The probe was attached to one of the legs of a tuning fork and vibrated using a piezoelectric buzzer to drive the tuning fork into the resonance state. When the probe was positioned away from the substrate, the vibration from the buzzer induced a voltage signal in the tuning fork due to the piezoelectric effect.…”

Biological Scanning Electrochemical Microscopy and Its Application to Live Cell Studies

“…[6][7][8][29][30][31] The inverted microscope confers several advantages to cell studies, including quick identification of healthy cells based on morphological changes and prepositioning of the UME close to cells, which reduces overall experimental time. Cell activity in the context of an SECM experiment is difficult to define and can imply the need for both direct and indirect modes of electrochemical detection.…”

Local Imaging of an Electrochemical Active/Inactive Region on a Conductive Carbon Surface by Using Scanning Electrochemical Microscopy

“…This technique is used for recognizing conductive and insulating surfaces and for imaging the insulator topography. 20,25,26 We imaged the patterned ECR nano-carbon film by using this SECM feedback mode with Ru(NH3)6 2+/3+ and Fe 2+/3+ mediators to image locally the electrochemical activity attributed to surface chemical functional groups. When the feedback mode is used with the Ru(NH3)6 3+ mediator, a current variation should be observed as a positive feedback signal in all regions, since ECR nano-carbon material has a homogeneously high conductivity (>20 S/cm) 16 and a high electron transfer rate, as observed in the voltammogram (Fig.…”