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

Wearable biosensors are garnering substantial interest due to their potential to provide continuous, real-time physiological information via dynamic, noninvasive measurements of biochemical markers in biofluids, such as sweat, tears, saliva and interstitial fluid. Recent developments have focused on electrochemical and optical biosensors, together with advances in the noninvasive monitoring of biomarkers including metabolites, bacteria and hormones. A combination of multiplexed biosensing, microfluidic sampling and transport systems have been integrated, miniaturized and combined with flexible materials for improved wearability and ease of operation. Although wearable biosensors hold promise, a better understanding of the correlations between analyte concentrations in the blood and noninvasive biofluids is needed to improve reliability. An expanded set of on-body bioaffinity assays and more sensing strategies are needed to make more biomarkers accessible to monitoring. Large-cohort validation studies of wearable biosensor performance will be needed to underpin clinical acceptance. Accurate and reliable real-time sensing of physiological information using wearable biosensor technologies would have a broad impact on our daily lives.

Wearable biosensors for healthcare monitoring.

Array-based vapour-sensing devices are used to detect and differentiate between chemically diverse analytes. These systems--based on cross-responsive sensor elements--aim to mimic the mammalian olfactory system by producing composite responses unique to each odorant. Previous work has concentrated on a variety of non-specific chemical interactions to detect non-coordinating organic vapours. But the most odiferous, toxic compounds often bind readily to metal ions. Here we report a simple optical chemical sensing method that utilizes the colour change induced in an array of metalloporphyrin dyes upon ligand binding while minimizing the need for extensive signal transduction hardware. The chemoselective response of a library of immobilized vapour-sensing metalloporphyrin dyes permits the visual identification of a wide range of ligating (alcohols, amines, ethers, phosphines, phosphites, thioethers and thiols) and even weakly ligating (arenes, halocarbons and ketones) vapours. Water vapour does not affect the performance of the device, which shows a good linear response to single analytes, and interpretable responses to analyte mixtures. Unique colour fingerprints can be obtained at analyte concentrations below 2 parts per million, and responses to below 100 parts per billion have been observed. We expect that this type of sensing array will be of practical importance for general-purpose vapour dosimeters and analyte-specific detectors (for insecticides, drugs or neurotoxins, for example).

A colorimetric sensor array for odour visualization

http://cau.ac.kr/~jjang14/BioMEMS/Ivnitski_BSBE_Bacteria_Detection_Bio_Sensors_Review_1999.pdf

Biosensors for detection of pathogenic bacteria

Humidity measurement is one of the most significant issues in various areas of applications such as instrumentation, automated systems, agriculture, climatology and GIS. Numerous sorts of humidity sensors fabricated and developed for industrial and laboratory applications are reviewed and presented in this article. The survey frequently concentrates on the RH sensors based upon their organic and inorganic functional materials, e.g., porous ceramics (semiconductors), polymers, ceramic/polymer and electrolytes, as well as conduction mechanism and fabrication technologies. A significant aim of this review is to provide a distinct categorization pursuant to state of the art humidity sensor types, principles of work, sensing substances, transduction mechanisms, and production technologies. Furthermore, performance characteristics of the different humidity sensors such as electrical and statistical data will be detailed and gives an added value to the report. By comparison of overall prospects of the sensors it was revealed that there are still drawbacks as to efficiency of sensing elements and conduction values. The flexibility offered by thick film and thin film processes either in the preparation of materials or in the choice of shape and size of the sensor structure provides advantages over other technologies. These ceramic sensors show faster response than other types.

/pdf/humidity-sensors-principle-mechanism-and-fabrication-q8mq7scozc.pdf

Humidity Sensors Principle, Mechanism, and Fabrication Technologies: A Comprehensive Review

. 1: Introduction. 1.1. The current mode approach: brief history of current conveyors. 1.2. The second generation current conveyor (CCII) as building block. 2: Design of CCII topologies. 2.1. CCII ideal and real characteristics and equivalent models. 2.2. CCII topologies: circuit schemes and electrical characteristics. 2.3. The CCII: state of the art and future trend. 3: CCII low voltage low power design and characteristics. 3.1. Design techniques for low voltage low power (LV LP). 3.2. Low voltage low power CCIIs. 3.4. Offset in current conveyors. 3.5. Noise in current conveyors. 4: Evolution of LV LP CCII basic building block. 4.1. Improvements of the basic CCII. 4.2. Towards the differential solutions. 5: LV LP CCII applications. 5.1. Basic applications. 5.2. Impedance simulators. 5.3. CCII-based filters. 5.4. Oscillators. 5.5. CCII applications. Appendix A. Appendix B. Appendix C.

https://www.springer.com/productFlyer_978-1-4020-7486-8.pdf?SGWID=0-0-1297-33340793-0

Low-Voltage Low-Power CMOS Current Conveyors

Since the first developments of electronic noses, food analysis has been considered as one of its most useful applications. In this paper an electronic nose based on quartz microbalances coated with metallo-porphyrins and related compounds is presented and illustrated. Extensive tests on various substances playing key roles in food analysis show that sensing properties of the sensing materials (in terms of sensitivity and selectivity) can be exploited for electronic nose applications devoted to the analysis of various kinds of foods. The versatility of this system has been successfully tested on different kinds of foods, such as fish, meat, vegetable and wine for which results are shown.

An electronic nose for food analysis

The application of metalloporphyrins as coating material for quartz microbalance-based chemical sensors

A novel floating inductance simulator, based on second generation current conveyors, is presented The circuit shows the capability of regulation and, in theory, cancellation of the undesired inductance series resistance, with consequent increase in the low frequency operating range Simulation results are included to prove the effectiveness of this solution

CCII-based floating inductance simulator with compensated series resistance

We propose a low-voltage (±1 V) low-power (3 mW) lock-in amplifier, fabricated in a standard CMOS technology (AMS 0.35 μm) with analog features and utilized for low-frequency gas sensor applications. The proposed lock-in architecture, which works at a fixed input signal frequency (77 Hz) with a very low input noise (only 34 nV/(sqrt(Hz)) @ 77 Hz), can be utilized to detect very small quantities of reagent gas, especially if combined with other techniques, as the sensor thermal modulation. The integrated solution has been fabricated on a single chip, requiring a reduced silicon area (about 5 mm 2 ). Experimental measurements have confirmed the capability of the proposed lock-in system to reveal very small signals, in particular, testing the whole system for gas detection, a resolution improvement by a factor valued about 50 allows to detect gas concentrations lower than 1 ppm.

Giuseppe Ferri

Papers

Low-Voltage Low-Power CMOS Current Conveyors

An electronic nose for food analysis

The application of metalloporphyrins as coating material for quartz microbalance-based chemical sensors

CCII-based floating inductance simulator with compensated series resistance

Low-voltage low-power integrated analog lock-in amplifier for gas sensor applications