Triangular silver nanoparticles (∼100 nm wide and 50 nm high) have remarkable optical properties. In particular, the peak extinction wavelength, λmax of their localized surface plasmon resonance (LSPR) spectrum is unexpectedly sensitive to nanoparticle size, shape, and local (∼10−30 nm) external dielectric environment. This sensitivity of the LSPR λmax to the nanoenvironment has allowed us to develop a new class of nanoscale affinity biosensors. The essential characteristics and operational principles of these LSPR nanobiosensors will be illustrated using the well-studied biotin−streptavidin system. Exposure of biotin-functionalized Ag nanotriangles to 100 nM streptavidin (SA) caused a 27.0 nm red-shift in the LSPR λmax. The LSPR λmax shift, ΔR/ΔRmax, versus [SA] response curve was measured over the concentration range 10-15 M < [SA] < 10-6 M. Comparison of the data with the theoretical normalized response expected for 1:1 binding of a ligand to a multivalent receptor with different sites but invariant af...

A nanoscale optical biosensor: sensitivity and selectivity of an approach based on the localized surface plasmon resonance spectroscopy of triangular silver nanoparticles.

Recent developments in the application of micro- and nanosystems for drug administration include a diverse range of new materials and methods. New approaches include the on-demand activation of molecular interactions, novel diffusion-controlled delivery devices, nanostructured 'smart' surfaces and materials, and prospects for coupling drug delivery to sensors and implants. Micro- and nanotechnologies are enabling the design of novel methods such as radio-frequency addressing of individual molecules or the suppression of immune response to a release device. Current challenges include the need to balance the small scale of the devices with the quantities of drugs that are clinically necessary, the requirement for more stable sensor platforms, and the development of methods to evaluate these new materials and devices for safety and efficacy.

Small-scale systems for in vivo drug delivery.

Since the late 1980s there have been spectacular developments in micromechanical or microelectro-mechanical (MEMS) systems which have enabled the exploration of transduction modes that involve mechanical energy and are based primarily on mechanical phenomena. As a result an innovative family of chemical and biological sensors has emerged. In this article, we discuss sensors with transducers in a form of cantilevers. While MEMS represents a diverse family of designs, devices with simple cantilever configurations are especially attractive as transducers for chemical and biological sensors. The review deals with four important aspects of cantilever transducers: (i) operation principles and models; (ii) microfabrication; (iii) figures of merit; and (iv) applications of cantilever sensors. We also provide a brief analysis of historical predecessors of the modern cantilever sensors.

Cantilever transducers as a platform for chemical and biological sensors

Stimuli-responsive polymer gels have received considerable attention due to their singular mechanical properties, which make them materials of choice for niche applications. Polymer gels comprising either physical or chemical cross-links can undergo controlled and reversible shape changes in response to an applied field. The stimulus or external field applied may include thermal, electrical, magnetic, pH, UV/visible light, ionic or metallic interactions or combinations thereof. The shape change can manifest itself in two-dimensional actuation, bending motion, or three-dimensional actuation, volume change. This reversible contraction and expansion of polymer gels as well as their mechanical properties are similar to that of biological muscles. This review will describe and critique some of the recent advances in the field of stimuli-responsive polymer gels including the design of new classes of polymeric gels, controlled actuation in response to external stimuli, and ability to tailor material properties for different applications.

Stimuli-responsive polymer gels

http://cau.ac.kr/~jjang14/BioMEMS/Bashir_ADDR_Reviews_BioMEMS_2004.pdf

BioMEMS: state-of-the-art in detection, opportunities and prospects

The application of microelectromechanical systems (MEMS) to medicine is described. Three types of biomedical devices are considered, including diagnostic microsystems, surgical microsystems, and therapeutic microsystems. The opportunities of MEMS miniaturization in these emerging disciplines are considered, with emphasis placed on the importance of the technology in providing a better outcome for the patient and a lower overall health care cost. Several case examples in each of these areas are described. Key aspects of MEMS technology as it is applied to these three areas are described, along with some of the fabrication challenges.

Microdevices in medicine.

The fabrication and structural characterization of a surface micromachined, resonant frequency, Pb(Zr, Ti)O3 (PZT) microcantilever will be presented. The PZT microcantilever was fabricated using surface micromachining techniques, and used a low-stress silicon nitride thin film as the base material for the microcantilever onto which a PZT thin film was incorporated. The PZT thin film is used as both the microsensor and the microactuator. A unique fabrication procedure was developed in order to eliminate the step of encapsulating the PZT during the removal of the spacer layer. The encapsulation step was avoided because of the difficulty in finding a suitable material, which would protect the PZT during the removal of the spacer layer yet not affect its material properties. This predicament was resolved by removing the spacer layer prior to the deposition of the PZT. The microcantilevers were characterized extensively using an atomic force microscope in an unusual manner. The atomic force microscope was modified in such a fashion that the deflection at the tip of the microcantilever could be measured as the frequency of an electrical signal applied to the PZT thin film was varied. In addition, an impedance analyzer was used to characterize the microcantilevers. Simple thin-film, laminated plate theory was used to obtain a closed-form solution for the modal response of the microcantilever, while ANSYS was used to obtain modal and harmonic simulation results. It will be shown that the experimental, numerical, and theoretical modal results are within ±10% of one another. The experimental and numerical harmonic results differ by an order of magnitude; however, the numerical model is currently being modified to more accurately represent the PZT microcantilever. From the information gathered during the structural characterization of the PZT microcantilever, it will be shown that certain higher-order resonant frequency modes have very large mechanical responses. These higher-order resonant frequency modes give designers another parameter to adjust when trying to optimize the design of their resonant frequency device.

https://iopscience.iop.org/article/10.1088/0964-1726/10/2/310/pdf

Fabrication and structural characterization of a resonant frequency PZT microcantilever

A miniaturized utility device 10 having integrated optical capabilities for use on a high aspect ratio system, wherein the miniaturized utility device 10 comprises: (a) a micro camera 14 comprising a solid state micro imaging device 84 including, as an integral structure, an imaging array 110 electrically coupled to a conductive pad 88, wherein the solid state imaging device 84 further includes at least one utility aperture 102 passing therethrough, and a lens 92 optically coupled to the imaging array 110; and (b) a micro utility instrument 18 configured for coordinated operation with the micro camera 14 at a common local site, wherein the micro utility instrument 18 is configured to perform a designated function viewable, preferably in real-time, via a camera image generated by the micro camera 14.

Miniaturized utility device having integrated optical capabilities

A silicon-based piezoelectric linear stepper motor has been designed and fabricated. The motor is based on an inertial drive concept derived from sequential electrostatic clamping and unclamping of a piezoelectric bar measuring 38.1/spl times/6.36/spl times/0.787 mm. The piezoelectric micromotor has been constructed and tested for precision surgical applications. The measured performance is dependent on the operating conditions selected. Representative performance is a speed of 1.2 mm/s against a 3.0 N load. The motor is limited in its travel by approximately the diameter of the silicon wafer used to fabricated it. The resolution of the motor is less than 100 nm in its most precise actuation mode.

Precision micromotor for surgery

Novel piezoelectric cantilever beams for micro sensors and actuators based on PZT thin films have been batch fabricated by surface micromachining. Lead zirconate titanate (PZT) thin film is formed by metalorganic deposition (MOD) on Pt/Ti/SiO2/Si (1 0 0) substrates and Pt/Ti/LTO/Si3N4 cantilever beams and then annealed at 700 °C in air. The PZT thin film is 0.5 μm thick and has dielectric permittivity of 1698, remanent polarization of 13.66 μC/cm2, and coercive field of 44.5 kV/cm. The influence of deposition temperatures on PZT thin film stress has been investigated. When continuously controlling the deposition temperatures, the stress of the thin film is reduced from 0.313 × 108 to 0.269 × 108 N/m, that is 16.4% decrease. With the total 120 designed devices on 4-inch wafers, the number of functional devices is increased from 82 to 97, that is 12.47%.

David T. Markus

Papers

Microdevices in medicine.

Fabrication and structural characterization of a resonant frequency PZT microcantilever

Miniaturized utility device having integrated optical capabilities

Precision micromotor for surgery

Piezoelectric thin films formed by MOD on cantilever beams for micro sensors and actuators