Mihai P. Dinca

Fast and accurate temperature control of a PCR microsystem with a disposable reactor

The paper presents a micro polymerase chain reaction (PCR) device consisting of a miniature thermal cycler incorporating Pt thin layers used as heater and temperature sensors, screen-printed on a ceramic plate and a disposable PDMS part with a 1 µl chamber. Using a heating power of only 0.3 W at 95 °C and 1.5 W during heating transitions, the device can provide a 7.7 °C s−1 heating rate. For temperature control, a two-degree-of-freedom proportional–integral–derivative controller in conjunction with an anti-windup algorithm was designed and implemented. The obtained performances (such as the use of the maximum/minimum power level during almost all of the transition time, overshoots and undershoots below 0.1 °C, very short settling time with no oscillation, steady error less than ±0.05 °C and excellent robustness against the process changes) exceed those published so far. In addition, the proposed controller is much simpler to implement and tune in comparison to other previously described controllers. A dynamical correction of the difference between the sensor and chamber temperatures is introduced and several profiles for set-point shaping are proposed and compared. The delayed preshaped profile, based on the inverse of the corresponding transfer function, was found to give the best results. Forced convection cooling is handled as a heat switch providing a cooling rate of 6.6 °C s−1 while preserving the low power requirement for heating. With the device described cycle times of 12 s (if the dwell times are not considered) are possible. PCR amplification with 32 cycles was successfully carried out in less than 25 min.

Ignition of an automobile engine by high-peak power Nd:YAG/Cr 4+ :YAG laser-spark devices.

Laser sparks that were built with high-peak power passively Q-switched Nd:YAG/Cr(4+):YAG lasers have been used to operate a Renault automobile engine. The design of such a laser spark igniter is discussed. The Nd:YAG/Cr(4+):YAG laser delivered pulses with energy of 4 mJ and 0.8-ns duration, corresponding to pulse peak power of 5 MW. The coefficients of variability of maximum pressure (COV(Pmax)) and of indicated mean effective pressure (COV(IMEP)) and specific emissions like hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO(x)) and carbon dioxide (CO2) were measured at various engine speeds and high loads. Improved engine stability in terms of COV(Pmax) and COV(Pmax) and decreased emissions of CO and HC were obtained for the engine that was run by laser sparks in comparison with classical ignition by electrical spark plugs.

Design of a PID Controller for a PCR Micro Reactor

Proportional-integral-derivative (PID) controllers are widely used in process control, and consequently they are described in most of the textbooks on automatic control. However, rather than presenting the overall design process, the examples given in such textbooks are intended to illuminate specific focused aspects of selection, tuning and implementation of the controller. This paper describes in detail the design of a PID controller for temperature control of a polymerase chain reaction (PCR) microreactor showing how different aspects, which necessarily are taught separately, interact in a real-world design. After setting the design targets by taking the hardware limitations into consideration, a continuous time controller, having two degrees of freedom, is designed by placing its dominant pair of poles using the root locus technique. Then, the integrator wind-up is addressed, the controller is translated into a discrete time version and, after implementation, the experimental performances are measured.

Multiple THz pulse generation with variable energy ratio and delay

Two methods for multiple high energetic THz pulse generation by two-color filamentation in air with controllable energy ratio and delay ranging from one to hundreds of ps were investigated. In the first method the laser pulse is split into two inside the optical stretcher of a CPA laser system, the resulting consecutive filaments occur in the same region and allows the study of the influence of the first plasma filament on the THz emission of the delayed filament. Based on a polarization sensitive thin film beam splitter placed in front of a 45° mirror, the second method produces multiple parallel consecutive filaments. Above a certain total pump level the THz energy delivered by multiple pulses exceeds the value given by a single filament for the same pump energy, thereby overcoming the THz emission saturation of the single filament.

The flexibility of hydrated bovine serum albumin investigated by THz spectroscopy and molecular modeling

The native cellular environment represents a crowded system comprising high concentrations of soluble molecules that interact mostly in a nonspecific manner. Some of the macromolecular crowding effects occurring in biological media are conformational changes and macromolecular associations. Most of our knowledge on protein folding and protein-protein interactions was acquired from experiments on proteins in dilute solutions or from theoretical models of isolated proteins in either explicit or implicit solvent. Here we present a 50% w/w bovine serum albumin (BSA) solution model that comprises two solute molecules included in a single water box. We determined the vibration spectrum of the 50% w/w BSA solution using THz spectroscopy and we calculated the theoretical THz spectrum. We observed a good correlation between the experimental and theoretical spectra for the frequency range of 0.3 - 1.5 THz. We also investigated the contribution of each BSA molecule to the solution THz spectrum by simulating THz spectra of the two BSA molecules from the solution model and water, each accounting for a 50% w/w BSA solution. The spectra appear to be similar. As the two molecules in our solution model have different conformations, we investigated the importance of the apparently insignificant differences between simulated THz spectra of the two proteins. We found that the differences should be considered significant, as they reflect differences between the flexibility of the two BSA molecules.

Dichroic mirror design by complete admittance matching

The application of a new admittance-matching method to the design of dichroic mirrors is presented. The method is based on the alteration of both thicknesses involved in the symmetrical period of the matching stack and provides the complete matching at the desired wavelength, i.e., both conditions for the equivalent admittance and phase thickness are fulfilled. A supplementary condition, stated for the derivative of the equivalent admittance with respect to the wavelength, produces a quasi-matching over a wide spectral range. A detailed description of the algorithm used by the computer program that performs this matching is given.

An integrated hybrid system for genetic analysis combining EWOD sample preparation and magnetic detection

Over the last decade microelectronic technologies have delivered significant advances in devices for point of care diagnostics. Complex microfluidic systems integrate components such as valves, pumps etc. to manipulate liquids. In recent years, the drive is to combine biochemical protocols in a single system, delivering sample in answer out. An Electrowetting on Dielectric (EWOD) device offers the possibility to move and manipulate 64nl volumes implementing biochemical processes, while the magnetic sensor facilitates hybridisation detection. We outline an injection molding approach where EWOD and magnetic devices are integrated into a hybrid microfluidic system with the potential to implement sample in answer out biological protocols.

3D protein structure determination by THz spectroscopy and molecular modelling: case study on bovine serum albumin

THz spectroscopy is a very powerful tool in investigating the vibrational modes and conformational transitions of biomolecules. Here we have used THz spectroscopy to study the vibrational spectrum of bovine serum albumin, a protein whose 3D structure is yet unknown. Experimental data were fitted with theoretical spectra obtained by normal modes analysis of BSA structures generated by homology modeling.

Interferential filter design with continuously variable refractive index

The paper briefly presents an original method for design of inhomogeneous thin films which takes into consideration from the beginning the finite character of the optical thickness. At the beginning, the best solution is obtained in terms of the value of a complex function on a certain spectral grid. At the second step, the design is converted in terms of refractive index profile. Special care is taken to minimize the variations of this profile. Then, a program using this method, written as Windows application, is described together with a design example providing a spectral dependence of the reflectance having the shape of Romanian Athenaeum building.

Admittance-matched interference polarizers

Abstract The paper reports the design and fabrication of a thin-film plate polarizer, working at λ = 1·064 μm. In order to obtain a broadening of the working spectral range, the design is made by using the method of optical admittance matching. The experimental conditions and the results are given.