David P. Fries

Underwater mass spectrometers for in situ chemical analysis of the hydrosphere

Underwater mass spectrometry systems can be used for direct in situ detection of volatile organic compounds and dissolved gases in oceans, lakes, rivers and waste-water streams. In this work we describe the design and operation of (1) a linear quadrupole mass filter and (2) a quadrupole ion trap mass spectrometer interfaced, in each case, with a membrane introduction/fluid control system and packaged for underwater operation. These mass spectrometry systems can operate autonomously, or under user control via a wireless rf link. Detection limits for each system were determined in the laboratory using pure solutions. The quadrupole mass filter system provides detection limits in the 1–5 ppb range with an upper mass limit of 100 amu. Its power requirement is approximately 95 Watts. The ion trap system has detection limits well below 1 ppb, an upper mass limit of 650 amu and MS/MS capability. Its power consumption is on the order of 150 Watts. The present membrane limits analysis to non-polar compounds (<300 amu) with analysis cycles of 5–15 minutes. Deployments of both types of instruments are described, along with a discussion of the challenges associated with in-water mass spectrometry and descriptions of alternative in-water mass spectrometer configurations.

Development of an underwater mass-spectrometry system for in situ chemical analysis

Progress in the design, construction and packaging of small portable mass spectrometers for operation on autonomous underwater vehicles (AUVs) is described. Our first deployable version consists of a membrane introduction interface coupled with a linear quadrupole mass filter for in situ detection and quantification of dissolved gases and volatile organic compounds. We present laboratory results which demonstrate that sub-parts-per-billion detection limits have been achieved for toluene. The mass-spectrometer system is compatible with AUV constraints and operates on 24 V dc, consuming of the order of 100 W of power. Technical challenges of performing underwater mass spectrometry are addressed, in particular sample introduction from the water column and the maintenance of a vacuum system. Initial operation will be in shallow water of 30 m depth or less. Alternative versions of interfaces and mass spectrometers are also discussed. We anticipate that providing the capability of performing in situ underwater mass-spectrometric analysis will have a significant impact in the areas of marine science and environmental monitoring.

A micro-fluidic galvanic cell as an on-chip power source

We present a micro-fluidics actuated galvanic cell for on demand power generation. The galvanic cell is an aluminum anode/alkaline electrolyte/air cathode cell. The concept is based upon an actuation mechanism that pushes an electrolyte into a micro-channel containing electrodes. When the electrolyte reaches the electrodes of a galvanic cell, it produces energy through an electrochemical reaction. The proof of concept is presented herein by fabricating and characterizing a single cell using micro-fabrication techniques. The actuation mechanism is based on the thermal expansion of a working fluid. A brief discussion on the optimization of this actuation is also presented. The open voltage of this micro-cell was experimentally measured to be around 1.9 V. The Al/air galvanic cell chemistry has been compared with commercial Zn/air battery and has been found to perform better. The present micro-cell design (with an area of 0.75 cm 2 ), is capable of providing an energy of 5 J after 6.0 min when subjected to a load of 20 � . The actuation mechanism takes less than a minute and consumes about 3.5 J.

A micromachined tunable CPW resonator

This paper presents a novel tunable microwave resonator, consisting of a CPW spiral inductor with a cantilever interconnect structure. Tuning was achieved by applying a DC bias between the input and output of the resonator circuit. An observable resonance tuning between 3 and 7 GHz was accomplished by applying a bias from 0 to 40 V. Corresponding Q-factors between 17 and 20 were obtained in this tuning range.

Spectrometric Determination of the Refractive Index of Optical Wave Guiding Materials Used in Lab-on-a-Chip Applications

The design and optimization of light-based analytical devices often require optical characterization of materials involved in their construction. With the aim of benefiting lab-on-a-chip applications, a transmission spectrometric method for determining refractive indices, n, of transparent solids is presented here. Angular dependence of the reflection coefficient between material–air interfaces constitutes the basis of the procedure. Firstly, the method is studied via simulation, using a theoretical algorithm that describes the light propagation through the sample slide, to assess the potentially attainable accuracy. Simulations also serve to specify the angles at which measurements should be taken. Secondly, a visible light source and an optical fiber spectrometer are used to perform measurements on three commonly used materials in optical lab-on-a-chip devices. A nonlinear regression subroutine fits experimental data to the proposed theoretical model and is used to obtain n. Because the attainable precision using this method of refractive index determination is dictated by the uncertainty in the transmission measurements, the precision (with 95% confidence) for mechanically rigid samples, namely glass and poly(methyl methacrylate) (PMMA), is higher than those estimated for the elastomer sample (in-house-molded poly(dimethylsiloxane) (PDMS)). At wavelengths with the highest signal-to-noise ratio for the spectrometer setup, the estimated refractive indices were 1.43 ± 0.05 (580 nm) for PDMS, 1.54 ± 0.02 (546 nm) for glass, and 1.485 ± 0.005 (656 nm) for PMMA. Accurate refractive index estimations with an average precision equal to 0.01 refractive index units (RIU) were obtained for PMMA and glass samples, and an average precision of 0.09 RIU for the PDMS molded slide between 550 and 750 nm was obtained.

A miniature, low cost CTD system for coastal salinity measurements

In this work we describe a small, low cost conductivity, temperature and depth (CTD) system for measurements of salinity in coastal waters. The system incorporates three low cost expendable sensors, a novel planar four-electrode conductivity cell, a planar resistive temperature device and a piezoelectric pressure sensor. The conductivity cell and the resistive temperature device were fabricated using novel printed circuit board (PCB) microelectromechanical (MEMS) techniques combined with a new thin-film material, liquid crystal polymer (LCP). Printed circuit board techniques allow for mass production of the sensors, thereby lowering the cost of the system. The three sensors are packaged so that they are independent of one another and can be quickly replaced if bio-fouled or damaged. Deployments in Bayboro Harbor, St Petersburg, FL demonstrate that the novel CTD systems are capable of obtaining highly resolved in situ salinity measurements comparable to measurements obtained using commercially available instruments. The estimated accuracies for the conductivity, temperature and pressure sensors are ±1.47%, ±0.546 °C and ±0.02 bar, respectively. This work indicates that a small, low cost CTD system with expendable/replaceable sensors can be used to provide accurate, precise and highly resolved conductivity, temperature and pressure measurements in a coastal environment.

PCB MEMS for environmental sensing systems

We are developing integrated microsystems and sensor networks for in-water measurements using PCB MEMS, also known as organic MEMS. The PCB MEMS laminates are based on liquid crystal polymers (LCP), polyimide (PI) and FR-4 materials with the various sensing elements made within or on top of the printed circuit substrates. Single layer, double layer, and laminate constructions have been achieved. The sensing systems that utilize this technology are directed toward chemical, biological and physical sensing devices. Recent progress in sensor development has yielded PCB MEMS sensors operating in the field. We have developed a multisensor system that measures conductivity, temperature and pressure, and a compact 3D system-in-package wireless module based on the 802.11b protocol. Combining the sensor and telemetry modules yields wireless sensor systems capable of being scaled into networks. The microsystems made in this economical PCB MEMS format can be utilized in the marine environment, especially in emerging adaptive sensor grids, but also be applied to terrestrial, atmospheric and industrial process control environments.

Hand-held thermal-regulating fluorometer

This article relates to the construction of a portable, low cost, thermal-regulating light-emitting diode (LED)-based, handheld fluorometer. This regulated fluorometer is based on both a low thermal mass infrared heater, and an orthogonal geometry LED-based filter fluorometer. Power is supplied through an external power supply and data is collected in real time through standard serial interfaces of personal computers or personal digital assistants. Thermal regulation is automatically maintained using temperature sensor feedback control. Optical excitation relies on LED light source(s) and optical detection is made through an adjustable integrating photodetector. With such a handheld system, applications requiring temperature sensitive photometric measurements for real-time analyte detection can be more easily performed in the field.

Sensitivity Tunable Inductive Fluid Conductivity Sensor Based on RF Phase Detection

New results are presented for a sensitivity-tunable, inductive fluid conductivity sensor based on RF phase detection. An electronically controlled RF phase shifter allows the sensor to function in a wide range of conductivities from 2-70 mS/cm and helps tune the sensitivity of the response in a selected conductivity range. The noncontact nature of the sensor makes it suitable for corrosive fluids. Furthermore, the small size of the sensing element (1 inch. Sq X 6 mm thick) makes it suitable for compact in-line and hand held monitoring systems.

A microfabrication strategy for cylindrical ion trap mass spectrometer arrays

This paper presents a microfabrication process for the realization of miniature cylindrical ion trap mass spectrometers, based on silicon MEMS technologies. In order to create these traps, several techniques are presented. Porous silicon etching technique resulting in vertical holes has been used to fabricate end-plates. The ring electrode (hole diameter 1.5 mm) has been fabricated using ultrasonic mechanical drill technique. Deep reactive ion etching (DRIE) was also used for fabrication of both ring electrode arrays and end-plate holes. The surfaces of the ring electrode and the end-plates have been made conducting by n+ doping. CYTOP films have been used both as a bonding layer and an insulator to bond the ring electrode to end-plates while ensuring electrical isolation. The thickness of CYTOP films has been chosen to ensure that it can withstand voltages up to 200 V while maintaining its bond strength.