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Sustainable agriculture is the answer to the rapid rise in food demand which is straining our soil, leading to desertification, food insecurity, and ecosystem imbalance. Sustainable agriculture revolves around having real-time soil health information to allow farmers to make the correct decisions. We present an ion-selective electrode (ISE) electrochemical soil nitrate sensor that utilizes electrochemical impedance spectroscopy (EIS) for direct real-time continuous soil nitrate measurement without any soil pretreatment. The sensor functionality, performance, and in-soil dynamics have been reported. The ion-selective electrode (ISE) is applied by drop casting onto the working electrode. The study was conducted on three different soil textures (clay, sandy loam, and loamy clay) to cover the range of the soil texture triangle. The non-linear regression models showed a nitrate-dependent response with R2 > 0.97 for the various soil textures in the nitrate range of 5–512 ppm. The validation of the sensor showed an error rate of less than 20% between the measured nitrate and reference nitrate for multiple different soil textures, including ones that were not used in the calibration of the sensor. A 7-day-long in situ soil study showed the capability of the sensor to measure soil nitrate in a temporally dynamic manner with an error rate of less than 20%.

Filopodia are thin finger-like protrusions from cells and they are hard to detect using electrical, mechanical, or optical sensors because of their nanometer scale features. Besides, the signals from filopodia and the cell membrane are often mixed together which makes the detection of filopodia challenging. Here, a 3D nanoplasmonic biosensor with microposts is proposed to overcome these limitations. By using suitable chemical coating and physical dimensions, the signals from filopodia and the cell membrane were separated by having the microposts keep the cell membrane from making contact with the nanoplasmonic biosensor. The filopodia were detected by the 3D asymmetrical nanopillars with sharp Fano resonance. The sensitivity and figure of merit of the nanoplasmonic biosensor were 650 nm per refractive index unit and 28.3, respectively. A large peak shift of 6 nm was observed for the detection of MC3T3 osteoblastic cell filopodia at a concentration of 1300 cells per mm2. To the best of our knowledge, this is the first demonstration of filopodia detection using nanoplasmonic biosensors, where microposts were used to separate the cell membrane from filopodia and the 3D nanoplasmonic biosensors were used to monitor filopodia on the nanometer scale. These combined 3D micro- and nano-structures allow filopodia to be detected using different sensors without interference from the cell membrane.

The world has migrated to portable applications ranging from smart phones to Lab on a Chip applications. However they come with a new set of challenges for analog IC designers. Low voltage operation, small area and low noise are the critical design criteria for portable devices. This paper presents a gm/ID based design methodology for low voltage current mode circuits using standard CMOS technology. A second generation current conveyor (CCII) and a current feedback operational amplifier (CFA) are designed using the discussed design procedure. Both circuits operate from a single 0.4 V supply. The CCII is used to implement an instrumentation amplifier. Multiple applications are implemented using the CFA. Post layout simulation using TSMC 90 nm and UMC 130 nm technology show that the presented design procedure is an attractive solution for low voltage CMOS current mode circuits.

This paper presents a low power instrumentation amplifier (IA) for the use in Internet of Things (IoT). A modified topology based on the INA321 by Texas Instruments of the two-opamp IA is used for its higher CMRR. The main design constraints are low power consumption and low noise. Two stage topology opamp is used for its capability of operating from a low supply voltage. Self-cascode technique enhances the open loop gain and allows the use of indirect compensation reducing the capacitor size. The drawback is reduced bandwidth however not a concern as many IoT applications exhibit narrow bandwidth. Post layout simulation is performed using Cadence Virtuoso 6.1.5 and TSMC 65 nm node. The designed opamp consumes 28.8 nW from a 0.4 V supply. Exhibits an open loop gain of 52 dB with phase margin 90 degrees. The IA has a fixed gain of 24 dB and bandwidth of 11 kHz. Common mode rejection of 83 dB is achieved. Total power dissipation is 89 nW.

Dielectrophoresis (DEP) is the phenomenon where a force is exerted on a particle when a non-uniform electric field is applied. It's commonly used in separating cancer cells from healthy cells or separating different strains of bacteria. DEP requires 2 perfectly out of phase signals with matched amplitude for controlling the electrical field. This paper presents a low power balanced signal generator based on the operational floating current conveyor (OFCC) for the use in lab-on-chips that use DEP levitation. The OFCC is a versatile analog current mode building block. The circuit is designed using standard TSMC 90 nm CMOS technology. The circuit consumes 11 μW from a 0.4 V single supply. The total chip area is 0.053 mm2. The generator outputs 2 signals with 0.03 dB difference in amplitude and 5 degrees in phase at 1 MHz. Post layout simulation show that the circuit provides a promising solution for Lab-on-Chip using DEP levitation techniques.

This paper describes the design of a low power current mode instrumentation amplifier dedicated to biomedical applications based on current conveyor. All MOSFETs operate in the subthreshold region yielding high energy efficiency using a single ended 0.4V supply. It's designed using standard CMOS technology which can be easily integrated into VLSI circuits. The design procedure is explained and verified by post layout results presented using TSMC 90 nm technology. Chopping technique is applied to reduce flicker noise to 3.59 μVrms for bandwidth 0.2–150 Hz. A high common mode rejection ratio of 107 dB is achieved while consuming 5.5 μW with maximum gain 41 dB. The chip area is 0.023 mm2. The obtained results demonstrate that well designed current mode circuits in subthreshold are an attractive solution for portable biomedical applications.

This paper presents a new low power Current Conveyor II (CCII). The proposed circuit uses a 0.4 V single-ended supply. The advantages of the proposed current mode readout circuit are threefold. Firstly, the proposed circuit provides extremely low power consumption while operating all MOSFETs in the subthreshold region providing the highest energy efficiency. Secondly, Self cascode technique is used to increase the gain of the differential amplifier to 65 dB. Finally, it is based on standard CMOS technology which can be easily used in VLSI circuits. Near perfect voltage/current tracking up to 1.25 / 0.8 MHz was achieved while consuming 1.7 μW.