There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Nanotechnology and biosensors

Pull-in instability as an inherently nonlinear and crucial effect continues to become increasingly important for the design of electrostatic MEMS and NEMS devices and ever more interesting scientifically. This review reports not only the overview of the pull-in phenomenon in electrostatically actuated MEMS and NEMS devices, but also the physical principles that have enabled fundamental insights into the pull-in instability as well as pull-in induced failures. Pull-in governing equations and conditions to characterize and predict the static, dynamic and resonant pull-in behaviors are summarized. Specifically, we have described and discussed on various state-of-the-art approaches for extending the travel range, controlling the pull-in instability and further enhancing the performance of MEMS and NEMS devices with electrostatic actuation and sensing. A number of recent activities and achievements methods for control of torsional electrostatic micromirrors are introduced. The on-going development in pull-in applications that are being used to develop a fundamental understanding of pull-in instability from negative to positive influences is included and highlighted. Future research trends and challenges are further outlined.

Electrostatic pull-in instability in MEMS/NEMS: A review

Textbook of biochemistry with clinical correlations , 4th edn TM Devlin, ed pp xvii + 1186, illustrated Wiley-Liss, New York, 1997 £2995, hardback

This beautifully illustrated and well-written book, with an impressive array of authors, is aimed at both undergraduate and postgraduate level As the editor states in the preface, it is not intended to be a compendium of biochemistry but rather emphasises the biochemistry of mammalian cells The first 22 chapters cover …

Textbook of biochemistry with clinical correlations

https://jcp.bmj.com/content/jclinpath/12/2/193.1.full.pdf

Practical Clinical Biochemistry

Aluminium coated polysilicon (Al-polySi) nanoresonator has been used to design a urea biosensor. The etching characteristic of Al by the ammonium hydroxide from urea hydrolysis in the presence of urease was used to estimate the urea concentration. Urease immobilized on Al coated polySi indicated smoothening of the surface with increasing urea concentration, confirming the etching of Al. The nanoresonator could estimate between 10-1000 nM concentrations of urea. The sensing was not affected in the presence of interferents such as uric acid and ascorbic acid, thus making it specific for urea. The sensor was found to be highly sensitive and specific and can have potential application in the field of medical diagnostics and environmental monitoring.

Detection of Urea and Ammonia with Aluminium Coated Polysilicon Nanoresonators

Conductivity of amorphous hydrogenated silicon in the planar and sandwich configurations

This paper discusses a simple electrical measurement technique to determine resonance frequency of surface
micromachined cantilever beams that is also suitable for packaged devices. Measurements are done on oxide anchored
doped polysilicon beams. If the beam is driven by an AC signal riding on the DC bias, the beam starts vibrating. When
the drive frequency matches the natural frequency of the beam, the oscillation amplitude is maximum. In this
measurement, the DC bias is fixed at a value lower than the pull-in voltage. A small AC bias is then applied such that the
sum of the DC and the maximum amplitude of the AC is less than the pull-in voltage. The frequency of the AC is then
swept and at resonance, because of large displacement, the beam is pulled in and this is detected by a current flowing
between the beam and the substrate. By iteratively adjusting the DC bias it is possible to make sure that pull-in occurs
only due to resonance and the frequency setting at this point gives the natural frequency of the beam. Measured values
for different beam lengths were compared with Doppler Vibrometry results and gave an excellent match.

Simple measurement technique for resonance frequency of micromachined cantilevers

Suitability of using ultrathin silicon nanoporous membranes (SNMs), fabricated using batch processes, for use in dialysis is investigated. In the present work, the diffusion of urea and creatinine through the SNMs were studied using two reservoirs containing the retentate and the permeate solution. Stirring of the solutions in the reservoirs was found to accelerate the diffusion process. Surface treatments on the SNM were carried out to prevent bio-fouling. Silanization followed by acid treatment was found to be the most effective method for preventing binding of urea on the SNM surface. Constant cycling in the trans-reservoir, maintained the concentration gradient of the dialysate and the diffusion increased significantly. The SNM appears to be a promising candidate for dialysis.

Functionalized Silicon Nanoporous Membranes for Efficient Dialysis

In a surface micromachined cantilever, the gap (g), beam thickness (t) and width get modified during fabrication. Since performance of sensors and actuators strongly depend on the final geometry, it becomes essential that these parameters are measured. Two sets of oxide anchored cantilever beams of different lengths with 20 and 30 mum widths are realised. On the released beams resonance frequency (fi) measurements are performed. For a given length, by finding the ratio between measured frequencies for two widths, we get the value of undercut. Using this value in the slope of a fi 2 versus L-4 plot we get the Young's modulus (E) of beam material.

Enakshi Bhattacharya

Papers

Detection of Urea and Ammonia with Aluminium Coated Polysilicon Nanoresonators

Conductivity of amorphous hydrogenated silicon in the planar and sandwich configurations

Simple measurement technique for resonance frequency of micromachined cantilevers

Functionalized Silicon Nanoporous Membranes for Efficient Dialysis

Electrical measurement of undercut in surface micromachined structures