A Highly Integrated Lab-on-a-CMOS Platform for Real-Time Monitoring of E. Coli Growth Kinetics.

Existing miniaturized and cost-effective solutions for bacterial growth monitoring usually require offline incubators with constant temperature to culture the bio-samples prior to measurement. Such a separated sample preparation and detection scheme requires extensive human intervention, risks contamination, and suffers from poor temporal resolution. To achieve integrated sample preparation and real-time bacterial growth monitoring, this article presents a lab-on-a-CMOS platform incorporates an optical sensor array, temperature sensor array, micro-heaters, and readout circuits. Escherichia coli's (E. coli) optimum growth temperature of 37 °C is achieved through a heat regulation system consisting of two micro-heaters and an on-chip temperature sensor array. A photodiode array with an in-pixel capacitive trans-impedance amplifier to reduce inter-pixel cross-coupling is designed to extract the optical information during bacterial growth. To balance the footprint, power consumption, and quantization speed, a 10 b column successive-approximation register (SAR)/single-slope (SS) dual-mode analog-to-digital converter (ADC) is designed to digitize the temperature and optical signals. Fabricated in a standard 0.18 um CMOS process, the proposed platform can regulate the sample temperature to 37 +/- 0.2/0.3 °C within 32 mins. Enabled by an on-chip heat regulation system and photodetectors, the prototype demonstrates a real-time monitoring of bacterial growth kinetics and antibiotic responses. Minute-level temporal resolution is achieved as this proposed platform is free of extensive and time-consuming human intervention. The proposed platform can be viably used in contamination sensitive applications such as antibiotic tests, stem cell cultures, and organ-on-chips.

Patching sulfur vacancies: A versatile approach for achieving ultrasensitive gas sensors based on transition metal dichalcogenides.

Transition metal dichalcogenides (TMDCs) garner significant attention for their potential to create high-performance gas sensors. Despite their favorable properties such as tunable bandgap, high carrier mobility, and large surface-to-volume ratio, the performance of TMDCs devices is compromised by sulfur vacancies, which reduce carrier mobility. To mitigate this issue, we propose a simple and universal approach for patching sulfur vacancies, wherein thiol groups are inserted to repair sulfur vacancies. The sulfur vacancy patching (SVP) approach is applied to fabricate a MoS2-based gas sensor using mechanical exfoliation and all-dry transfer methods, and the resulting 4-nitrothiophenol (4NTP) repaired molybdenum disulfide (4NTP-MoS2) is prepared via a sample solution process. Our results show that 4NTP-MoS2 exhibits higher response (increased by 200 %) to ppb-level NO2 with shorter response/recovery times (61/82 s) and better selectivity at 25 °C compared to pristine MoS2. Notably, the limit of detection (LOD) toward NO2 of 4NTP-MoS2 is 10 ppb. Kelvin probe force microscopy (KPFM) and density functional theory (DFT) reveal that the improved gas sensing performance is mainly attributed to the 4NTP-induced n-doping effect on MoS2 and the corresponding increment of surface absorption energy to NO2. Additionally, our 4NTP-induced SVP approach is universal for enhancing gas sensing properties of other TMDCs, such as MoSe2, WS2, and WSe2.

Large-Area and Visible-Light-Driven Heterojunctions of In2O3/Graphene Built for ppb-Level Formaldehyde Detection at Room Temperature.

Achieving convenient and accurate detection of indoor ppb-level formaldehyde is an urgent requirement to ensure a healthy working and living environment for people. Herein, ultrasmall In2O3 nanorods and supramolecularly functionalized reduced graphene oxide are selected as hybrid components of visible-light-driven (VLD) heterojunctions to fabricate ppb-level formaldehyde (HCHO) gas sensors (named InAG sensors). Under 405 nm visible light illumination, the sensor exhibits an outstanding response toward ppb-level HCHO at room temperature, including the ultralow practical limit of detection (pLOD) of 5 ppb, high response (Ra/Rg = 2.4, 500 ppb), relatively short response/recovery time (119 s/179 s, 500 ppb), high selectivity, and long-term stability. The ultrasensitive room temperature HCHO-sensing property is derived from visible-light-driven and large-area heterojunctions between ultrasmall In2O3 nanorods and supramolecularly functionalized graphene nanosheets. The performance of the actual detection toward HCHO is evaluated in a 3 m3 test chamber, confirming the practicability and reliability of the InAG sensor. This work provides an effective strategy for the development of low-power-consumption ppb-level gas sensors.

Assembly of Core/Shell Nanospheres of Amorphous Hemin/Acetone-Derived Carbonized Polymer with Graphene Nanosheets for Room-Temperature NO Sensing.

Implementing parts per billion-level nitric oxide (NO) sensing at room temperature (RT) is still in extreme demand for monitoring inflammatory respiratory diseases. Herein, we have prepared a kind of core-shell structural Hemin-based nanospheres (Abbr.: Hemin-nanospheres, defined as HNSs) with the core of amorphous Hemin and the shell of acetone-derived carbonized polymer, whose core-shell structure was verified by XPS with argon-ion etching. Then, the HNS-assembled reduced graphene oxide composite (defined as HNS-rGO) was prepared for RT NO sensing. The acetone-derived carbonized polymer shell not only assists the formation of amorphous Hemin core by disrupting their crystallization to release more Fe-N4 active sites, but provides protection to the core. Owing to the unique core-shell structure, the obtained HNS-rGO based sensor exhibited superior RT gas sensing properties toward NO, including a relatively higher response (Ra/Rg = 5.8, 20 ppm), a lower practical limit of detection (100 ppb), relatively reliable repeatability (over 6 cycles), excellent selectivity, and much higher long-term stability (less than a 5% decrease over 120 days). The sensing mechanism has also been proposed based on charge transfer theory. The superior gas sensing properties of HNS-rGO are ascribed to the more Fe-N4 active sites available under the amorphous state of the Hemin core and to the physical protection by the shell of acetone-derived carbonized polymer. This work presents a facile strategy of constructing a high-performance carbon-based core-shell nanostructure for gas sensing.

A Novel Design Nomogram for Optimization of Micro Search Coil Magnetometer for Energy Monitoring in Smart Buildings.

In this paper, a new analytical method to achieve the maximum signal-to-noise ratio (SNR) of a micro search coil magnetometer (µSCM) is presented. A planar spiral inductor was utilized to miniaturize conventional bulky search coil magnetometers. First, dimensional analysis was applied to identify three dimensionless parameters for the µSCM's key performance indices (sensitivity (Se), noise, and SNR). The effect of the parameters on the µSCM's performance was carefully investigated, and a novel 4D nomogram was developed. Furthermore, an SNR analysis considering noise sources of a low-noise amplifier was performed. By combining the results from the nomogram and the effect of the noise sources from the amplifier circuit, optimum values for the dimensionless parameters were calculated. According to the calculation results, the dominant noise source varied with an increase in the track width ratio to the outer diameter. Seven different samples were fabricated by a single-mask lithography process. The sensitivity of 1612 mV/mT was demonstrated at a 50 Hz input magnetic field, which was better than the previous µSCM (Se = 6.5 mV/mT) by more than 2 orders of magnitude. Finally, one of the fabricated µSCMs was employed to measure the online power consumption of a personal computer while different types of software were running.

Carbon Dots Embedded in Cellulose Film: Programmable, Performance-Tunable, and Large-Scale Subtle Fluorescent Patterning by in Situ Laser Writing.

Fluorescent patterns with multiple functions enable high-security anti-counterfeiting labels. Complex material synthesis and patterning processes limit the application of multifunctional fluorescent patterns, so the technology of in situ fluorescent patterning with tunable multimodal capabilities is becoming more necessary. In this work, an in situ fluorescent patterning technology was developed using laser direct writing on solid cellulose film at ambient conditions without masks. The fluorescent intensity and surface microstructure of the patterns could be adjusted by programmable varying of the laser parameters simultaneously. During laser direct writing, carbon dots are generated in situ in a cellulose ester polymer matrix, which significantly simplifies the fluorescent patterning process and reduces the manufacturing cost. Interestingly, the tunable fluorescent intensity empowers the fabrication of visual stereoscopic fluorescent patterns with excitation dependence, further improving its anti-counterfeiting performance. The obtained fluorescent patterns still show ultrahigh optical properties after being immersed in an acid/base solution (pH 5-12) over one month. In addition, the anti-UV performance of the obtained laser-patterned film with transmittance around 90% is comparable to that of commercial UV-resistant films. This work provided an advanced and feasible approach to fabricating programmable, performance-tunable, subtle fluorescent patterns in large-scale for industrial application.

A smartphone-based electroporation system with highly robust and low-voltage silicon nanopillar chips.

In this work, a novel smartphone-based electroporation (EP) system integrated with 3D scalable and robust gold-coated silicon-nanopillar Electroporation (Au-Si NP-EP) chip using projection photolithography is developed, for the first time, for both EP and electric cell lysing (ECL) at low voltages. Au-SiNP-EP chip consists of silicon nanopillars fabricated by using ASML stepper, Deep Reactive Ion Etching (DRIE) process and coated with a gold microelectrode. The silicon nanopillars were optimized based on theoretical analysis and numerical simulations to enhance the electrical field intensity and mechanical strength. The fabricated Au-SiNP-EP chips are tested with both permeable (Acridine Orange (AO) and impermeable (Propidium Iodide (PI)) molecules for HeLa cells at different volts (1-8 V) and pulse duration (1-9 µs). The fabricated chip achieved an optimized EP efficiency of 84.3% and cell viability of 81.4% at a much smaller voltage (4.5V) than reported planar electroporation (PEP) devices (8-100V). Compared with nanostructures-based devices (2-20 V), our devices show both higher mechanical strength and fabrication yield. Besides, a smartphone app integrated with a low-cost open-source portable Arduino-based system is developed to provide optimized electrical protocols for both EP and ECL. The electric cell lysing with ECL efficiency of 97.0% at 7 V and pulse duration of 9 ms has been successfully demonstrated. The experimental results show that the proposed smartphone-based EP system with Au-SiNP EP chips is promising for various applications, including intracellular delivery of various biomolecules, drugs, and release of DNA/RNA molecules from biological cells.

An Optical and Temperature Assisted CMOS ISFET Sensor Array for Robust E. Coli Detection.

Both bacterial viability and concentration are significant metrics for bacterial detection. Existing miniaturized and cost-effective single-mode sensor, pH or optical, can only be skilled at detecting single information viability or concentration. This paper presents an inverter-based CMOS ion-sensitive-field-effect-transistor (ISFET) sensor array, featuring bacterial pH detection which is an indicator of viability. The proposed design realizes pH detection using the native passivation layer of CMOS process as a sensing layer and configuring an inverter-based front-end as a capacitive feedback amplifier. This sensor array is assisted by temperature sensing and optical detection which reveals bacterial concentration. The optical detection is enabled using the leakage current of a reset switch as a response to a light source. While in reset mode, the inverter-based amplifier works as a temperature sensor that could help to reduce temperature influences on pH and optical detection. All the functionalities are realized using one single inverter-based amplifier, resulting in a compact pixel structure and largely relaxed design complexity for the sensor system. Fabricated in 0.18 µm standard CMOS process, the proposed CMOS sensor array system achieves an amplified pH sensitivity of 221 mV/pH, an improved sensor resolution of 0.03 pH through systematic noise optimization, a linear optical response, and a maximum temperature error of 0.69 °C. The sensing capabilities of the proposed design are demonstrated through on-chip Escherichia coli (E. coli) detection. This study may be extended to a rapid and cost-effective platform that renders multiple information of bacterial samples.

A High Offset Distribution Tolerance High Resolution ISFET Array With Auto-Compensation for Long-Term Bacterial Metabolism Monitoring.

This paper presents a CMOS ion-sensitive-field-effect-transistor (ISFET) array with superior offset distribution tolerance, resolution and linearity for long-term bacterial metabolism monitoring. A floating gate ISFET is adopted as the sensing front end to maximize ion sensitivity and support ultra-long-term measurement. To solve the DC offset issue induced by trapped chargers and drifts in each ISFET sensor, a complementary readout scheme with column offset compensation is proposed. P-type and N-type source followers are combined to cover a wide range of input DC offsets while maintaining small area and high linearity. The DC offset is digitally compensated during signal readout to facilitate global amplification and quantization. Fabricated in 0.18 µm standard CMOS process, the ISFET array can tolerate an offset distribution beyond power supply with a linear pH-to-output response. Due to high ion sensitivity and low circuit noise, the whole system achieves a high resolution of 0.017 pH. The proposed ISFET system has successfully demonstrated an accurate pH monitoring of normal Escherichis coli growth for 11 hours and its response to antibiotics, showing long-term bacterial metabolism monitoring capability.

The synergy of chemical immobilization and electrical orientation of T4 bacteriophage on a micro electrochemical sensor for low-level viable bacteria detection via Differential Pulse Voltammetry.

In this work, a wild-type T4 bacteriophage based micro electrochemical sensor (T4B-MES) was developed for specific and sensitive detection of viable pathogenic bacteria. Recently, bacteriophage has been widely applied as recognition elements for bacteria detection due to its low cost, high stability and specificity. Firstly, a systematic study was proposed in this paper to investigate the synergy of externally applied electric field and chemical functionalization on phage immobilization, involving several key factors such as Debye length. According to our experiments, the capture efficiency of the deposited phages had reached the maximum when the Debye length was comparable to the phage size. With the optimized immobilization protocol, the sensitivity of the T4B-MES was then determined with Differential Pulse Voltammetry (DPV), providing a quite low detection limit of 14 ± 5 cfu/mL and a wide dynamic range of 1.9 × 101-1.9 × 108 cfu/mL. In addition, the T4B-MES demonstrated the ability to distinguish viable and dead bacteria cells with high specificity, making it a promising solution in a variety of applications, e.g., water quality monitoring.

Phage-based Electrochemical Sensors: A Review.

Phages based electrochemical sensors have received much attention due to their high specificity, sensitivity and simplicity. Phages or bacteriophages provide natural affinity to their host bacteria cells and can serve as the recognition element for electrochemical sensors. It can also act as a tool for bacteria infection and lysis followed by detection of the released cell contents, such as enzymes and ions. In addition, possible detection of the other desired targets, such as antibodies have been demonstrated with phage display techniques. In this paper, the recent development of phage-based electrochemical sensors has been reviewed in terms of the different immobilization protocols and electrochemical detection techniques.

Direct label-free protein detection in high ionic strength solution and human plasma using dual-gate nanoribbon-based ion-sensitive field-effect transistor biosensor.

We report on direct label-free protein detection in high ionic strength solution and human plasma by a dual-gate nanoribbon-based ion-sensitive field-effect transistor (NR-ISFET) biosensor system with excellent sensitivity and specificity in both solution-gate (SG) and dual-gate (DG) modes. Compared with previously reported results, the NR-ISFET biosensor enables selective prostate specific antigen (PSA) detection based on antibody-antigen binding in broader detection range with lower LOD. For the first time, real-time specific detection of PSA of 10 pM to 1 µM in 100 mM phosphate buffer (PB) was demonstrated by conductance measurements using the polyethylene glycol (PEG)-modified NR-ISFET biosensors in DG mode with the back-gate bias (VBG) of 20 V. Due to larger maximum transconductance value resulting from the modulation of NR-ISFET channel by the back gate in DG mode, the detection range can be broadened with larger linear detection region (100 pM to 100 nM) and lower limit of detection (LOD, 10 pM) as compared to those in SG mode. Moreover, the influence of different back-gate bias from VBG = 5 V to VBG = 25 V on the biosensor performance has been investigated. Furthermore, direct PSA detection of 100 pM to 1 µM in human plasma was demonstrated by using the PEG-modified NR-ISFET in DG mode, enabling direct detection of protein in human blood for clinical applications since the LOD of 100 pM PSA can meet the clinical requirements.

A novel combination of four flavonoids derived from Astragali Radix relieves the symptoms of cyclophosphamide-induced anemic rats.

By using a feedback system control scheme, the best combination of formononetin, ononin, calycosin, and calycosin-7-O-ß-d-glucoside derived from Astragali Radix was shown to activate a hypoxia response element, a regulator for erythropoietin (EPO) transcription, in kidney fibroblast. In cyclophosphamide-induced anemic rats, the treatment of combined flavonoids, or EPO, improved the levels of red blood cells, white blood cells, hemoglobin, and hematocrit. In addition, the altered levels of antioxidant capacity, super oxidase dismutase, and malondialdehyde, triggered in anemic rats, were restored to control levels by the treatment of flavonoids. Here, we proposed a possible therapy by using the common flavonoids in treating anemia.

A Nonlinear Size-Dependent Equivalent Circuit Model for Single-Cell Electroporation on Microfluidic Chips.

Electroporation (EP) is a process of applying a pulsed intense electric field on the cell membrane to temporarily induce nanoscale electropores on the plasma membrane of biological cells. A nonlinear size-dependent equivalent circuit model of a single-cell electroporation system is proposed to investigate dynamic electromechanical behavior of cells on microfluidic chips during EP. This model consists of size-dependent electromechanical components of a cell, electrical components of poration media, and a microfluidic chip. A single-cell microfluidic EP chip with 3D microelectrode arrays along a microchannel is designed and fabricated to experimentally analyze the permeabilization of a cell. Predicted electrical current responses of the model are in good agreement (average error of 6%) with that of single-cell EP. The proposed model can successfully predict the time responses of transmembrane voltage, pore diameter, and pore density at four different stages of permeabilization. These stages are categorized based on electromechanical changes of the lipid membrane. The current-voltage characteristic curve of the cell membrane during EP is also investigated at different EP stages in detail. The model can precisely predict the electric breakdown of different cell lines at a specific critical cell membrane voltage of the target cell lines.

Optimizing combinations of flavonoids deriving from astragali radix in activating the regulatory element of erythropoietin by a feedback system control scheme.

Identifying potent drug combination from a herbal mixture is usually quite challenging, due to a large number of possible trials. Using an engineering approach of the feedback system control (FSC) scheme, we identified the potential best combinations of four flavonoids, including formononetin, ononin, calycosin, and calycosin-7-O- ß -D-glucoside deriving from Astragali Radix (AR; Huangqi), which provided the best biological action at minimal doses. Out of more than one thousand possible combinations, only tens of trials were required to optimize the flavonoid combinations that stimulated a maximal transcriptional activity of hypoxia response element (HRE), a critical regulator for erythropoietin (EPO) transcription, in cultured human embryonic kidney fibroblast (HEK293T). By using FSC scheme, 90% of the work and time can be saved, and the optimized flavonoid combinations increased the HRE mediated transcriptional activity by ~3-fold as compared with individual flavonoid, while the amount of flavonoids was reduced by ~10-fold. Our study suggests that the optimized combination of flavonoids may have strong effect in activating the regulatory element of erythropoietin at very low dosage, which may be used as new source of natural hematopoietic agent. The present work also indicates that the FSC scheme is able to serve as an efficient and model-free approach to optimize the drug combination of different ingredients within a herbal decoction.

Single-cell electroendocytosis on a micro chip using in situ fluorescence microscopy.

Electroendocytosis (EED), i.e. electric field-induced endocytosis, is a technique for bio-molecule and drug delivery to cells using a pulsed electric field lower than that applied in electroporation (EP). Different from EP in which nanometer-sized electropores appear on the plasma membrane lipid bilayer, EED induces cell membrane internalization and fission via endocytotic vesicles. In this study, we conduct comprehensive experimental study on the EED of HeLa cells using a micro chip and the corresponding endocytotic vesicles were visualized and investigated by using FM4-64 fluorescent dye and in situ fluorescence microscopy. The uptake of molecules by the EED of cells was characterized by average intracellular fluorescent intensity from a large number (>2,000) of single cells. The EED efficiency was determined as a function of three electric parameters (electric field strength, pulse duration, total electric treatment time). The EED efficiency as a function of electric field strength clearly shows biphasic characteristics at different experimental conditions. The EED experiments using cytoskeleton inhibitors illustrate unique mechanisms distinct from EP. This study provides a foundation for further on-chip study of the time-dependent mechanism of EED at the single-cell level.

Effects of deformability and thermal motion of lipid membrane on electroporation: by molecular dynamics simulations.

Effects of mechanical properties and thermal motion of POPE lipid membrane on electroporation were studied by molecular dynamics simulations. Among simulations in which specific atoms of lipids were artificially constrained at their equilibrium positions using a spring with force constant of 2.0 kcal/(molŲ) in the external electric field of 1.4 kcal/(molŠe), only constraint on lateral motions of lipid tails prohibited electroporation while non-tail parts had little effects. When force constant decreased to 0.2 kcal/(molŲ) in the position constraints on lipid tails in the external electric field of 2.0 kcal/(molŠe), water molecules began to enter the membrane. Position constraints of lipid tails allow water to penetrate from both sides of membrane. Thermal motion of lipids can induce initial defects in the hydrophobic core of membrane, which are favorable nucleation sites for electroporation. Simulations at different temperatures revealed that as the temperature increases, the time taken to the initial pore formation will decrease.

Effects of embedded sub-micron pillar arrays in microfluidic channels on large DNA electrophoresis.

A study of the influences of embedding artificial structures in a microfluidic device for CE with a free buffer solution is presented. Compared with conventional slab-gel electrophoresis, three major additional effects on the overall system performance are identified when sub-micron pillar arrays are integrated into a standard CE microsystem. Since DNA molecules have to migrate in-between and interact with the pillars, pillar geometry is first demonstrated to have a direct impact on the DNA motion pattern. Electric field re-distribution is another inevitable outcome when features of sub-micron dimensions are placed inside a microchannel. This effect is verified by a numerical simulation tool. Furthermore, the integration of the closely packed sub-micron structures dramatically increases the surface to volume ratios in the microfluidic device and therefore generates a large EOF. The consequence of these additional influences implies a complexity in the measured DNA velocity and indicates that careful considerations have to be taken when these devices are used for DNA electrokinetics study or electrophoresis theory re-examination.

Nonlinear current response of micro electroporation and resealing dynamics for human cancer cells.

This paper presents a novel method to measure the dynamic process of membrane permeability during electroporation (EP) on microchips for human cancer cells. Micro EP chips with three-dimensional gold electrodes accommodating a single cell in between were fabricated with a modified electroplating process. Electrochemical impedance spectroscopy (EIS) was carried out with an electrochemistry analyzer on micro EP chips and a nonlinear equivalent circuit model was proposed to describe the dynamic response of the whole system. Using such a method, micro EP current was isolated from undesired leakage current to study the corresponding electroporation dynamics under different input voltages. In addition, cell membrane recovery dynamics after electroporation was also studied and the resealing time constants were determined for different pulse treatments.