(490g) Fabrication of SOLID State MICRO and Nanopores on a Silicon Substrate – Controlled Electrochemical Method

 

M. Vega¹, G. Rosero², M. Der², P. Granell³, B. Lerner², C. Lasorsa², M.S. Perez²and E.M Martín del Valle¹

¹Department of Chemical Engineering, University of Salamanca, P/Los Caídos S/N, 37008, Spain

^ 2National Technological University (UTN), Buenos Aires, 1076, Argentina

³INTI-CMNB, San Martín, Buenos Aires, Argentina.

^ 

In recent years, the first sequencer of DNA based on nanopores has come on the market [1]. It fits in the palm of a hand, has the ability to read fragments up to 100 kb and does not require PCR amplification, among other qualities. Because of its low cost, this device promises to revolutionize the field of DNA sequencing and medicine, and shows the importance of research in an area such as the nanopores and their contribution to the field of nanoscience and nanotechnology.

This work presents results corresponding to the study of the fabrication process of solid state micro and nanopores by wet etching steps on crystalline silicon wafers [2]. A first etching was performed simultaneously on both sides of the wafers using 7M KOH at 80°C. Subsequently, a second etching was carried out by neutralization etchant (KOH) with a strong acid (HCl) or weak acid (HCOOH), applying electric potential. Pt electrodes were put into the KOH and acid solutions respectively and connected to a source meter instrument (keithley 2612), applying electric potential allowing ions exchange tween the KOH and acid solutions.

During the second etching step, silicon is etched by the hydroxyl ions in the etchant to generate silicon hydroxide and free electrons. Therefore, the anode attracts the hydroxyl ions so that the etching rate can be slowed down and a more precise nanopore can be fabricated. In general, a nano scale pore should allow both the cation (K­⁺ 0.137nm) and anions (Cl^- 0.181 nm) penetrate simultaneously. However, due to the electric osmosis inside a nanopore, the ion diffusion induced current becomes too slight to be efficiently detected.

A thorough characterization of the method is performed and the behavior of the attacking agent gent, as well as the action of formic acid and hydrochloric acid as braking agents is analyzed under different temperatures (64, 84 Ë?C) and electric potential (0.1, 0.5, 1 V) conditions. An applied electric potential is thus needed to drive the ions traveling through the nanopore to enable real time monitoring of the nanopore formation with measurements of temporal evolution of currents. After of the nanopore or micropore fabrication salts formation was noticed on crystalline silicon wafers that a priori can block the nanopore or micropore, however, with formic acid lower salt concentrations were detected. It was also observed that the higher the voltage and temperatura applied, the greater the etching process velocity, being the process dependent on these parameters. Results obtained showed that the pore size was adjusted by controlling the reaction temperature and electric potential. In summary, different etching stages are recognized and, in order to establish the pore formation time, possible parameters and useful dependences are determined. Also, the fate of the applied potential during etching process is studied, analyzing the effect of the potential magnitude under etching rate, neutralization and pore diameters of pores obtained during the process performance.

REFERENCES

1. Ashton, P.M., et al., MinION nanopore sequencing identifies the position and structure of a bacterial antibiotic resistance island. Nature Biotechnology, Vol. 33 (2014) No. 296-300.

2. Vega, M. Lerner, B. Lasorsa, C. Pierpauli, K. Perez, M. â??Automated and low cost method to manufacture addressablesolid-state nanoporesâ? Microsyst Technol, Vol. 22 (2014), Issue 1, p 109-117.