CHEMICAL SENSORS
A living cell can pick a single potassium ion out of a crowded solution of chemically similar neighbours, using protein channels only a few angstroms wide. Reproducing that degree of discrimination in a manufactured device is one of the central challenges of analytical chemistry, and it is the problem that drives our chemical sensing research. At the Asadnia Group, we design ion-selective materials, membranes and electrodes that identify a target species with high specificity, then package them into robust, low-cost and field-deployable instruments for water, agriculture, energy and clinical use.
A living cell can pick a single potassium ion out of a crowded solution of chemically similar neighbours, using protein channels only a few angstroms wide. Reproducing that degree of discrimination in a manufactured device is one of the central challenges of analytical chemistry, and it is the problem that drives our chemical sensing research. At the Asadnia Group, we design ion-selective materials, membranes and electrodes that identify a target species with high specificity, then package them into robust, low-cost and field-deployable instruments for water, agriculture, energy and clinical use.
Transistor-Based Ion Sensing
Conventional ion-selective electrodes are accurate but fragile: they depend on a reference electrode and an internal filling solution, which makes them difficult to miniaturise and unsuitable for long deployments in the field. We addressed this by combining ion-selective polymer membranes with AlGaN/GaN high-electron-mobility transistors, a wide-bandgap semiconductor platform that is chemically stable and inherently rugged. Using this architecture, we demonstrated selective detection of mercury (II), a metal that causes irreversible damage to human, animal and plant life, and of calcium ions, both with ionophore-doped PVC membranes deposited directly onto the transistor gate. Alongside the devices we developed the underlying theory, publishing a description of ionophore-doped membranes with a blocked interface that explains how these sensors respond over time.
Metal-Organic Frameworks Against Sensor Drift
The main obstacle to long-term potentiometric sensing is drift at the solid contact, where ionic signal must be converted into an electronic signal. We introduced metal-organic frameworks (MOFs) as ion-to-electron transducers for this interface, first in a highly stable lithium-selective electrode and more recently using conductive MOFs designed specifically to suppress drift. This work has been translated into a portable multiplexed ion-selective sensor for continuous, long-term monitoring of irrigation water quality, allowing growers to track nutrient and salinity levels in situ rather than sending samples to a laboratory.
Angstrom-Engineered Membranes for Lithium
Demand for lithium is expected to outstrip supply, making its selective recovery from brines and seawater a strategic priority. Because lithium, sodium and potassium ions are almost indistinguishable in size and charge, separating them requires control of channel chemistry and geometry at the angstrom scale. We have built such channels in graphene oxide nanosheets loaded with natural lithium-ion trappers, in MXene membranes tuned through their interlayer d-spacing, and in carboxylate-functionalised UiO-66 films with programmable ionic pathways. Our asymmetric MOF-on-MOF design, in which a bilayer structure narrows from 6 to 3.4 angstroms, produced an ionic current rectification ratio above 100 and selectivity ratios of 84 for K⁺/Li⁺ and 80 for Na⁺/Li⁺, among the highest reported for monovalent ion separation.
From Selectivity to Energy
The same nanochannels that separate ions can also generate power. Where a river meets the sea, the salinity gradient stores a large amount of recoverable energy, and a membrane that passes one ion while blocking its counter-ion converts that gradient into electricity. Our bioinspired heterogeneous MOF-on-MOF membrane delivered an output power density of 40.01 W/m² under a 500-fold concentration gradient and 9.20 W/m² with real sea and river water. We are extending this work with amphoteric zirconium-based MOF membranes and chelating-resin-modified polymers for sustainable osmotic energy generation.
Biosensing and Clinical Chemistry
Chemical sensing also has a place inside the body. We recently developed a miniaturised electrochemical biosensor for real-time in vivo monitoring of potassium in the inner ear, where ionic composition is tightly linked to hearing and balance function. Related projects include ZIF-8 photonic crystal biosensors for blood component recognition, MOF-based enzymatic microfluidic biosensors created by surface patterning and biomineralisation, and fluorescent carbon nanospheres for mercury detection in contaminated water.
Cleaner Water and Faster Discovery
Complementing the sensors, we develop low-cost natural clay and ceramic membranes for treating dye effluent, mine washery waste and aquaculture wastewater, and nanomembranes for capturing hazardous cations. Across all of these projects, we increasingly use machine learning to accelerate the discovery of ion-selective materials, an approach summarised in our edited volume Artificial Intelligence and Data Science in Environmental Sensing.
Conventional ion-selective electrodes are accurate but fragile: they depend on a reference electrode and an internal filling solution, which makes them difficult to miniaturise and unsuitable for long deployments in the field. We addressed this by combining ion-selective polymer membranes with AlGaN/GaN high-electron-mobility transistors, a wide-bandgap semiconductor platform that is chemically stable and inherently rugged. Using this architecture, we demonstrated selective detection of mercury (II), a metal that causes irreversible damage to human, animal and plant life, and of calcium ions, both with ionophore-doped PVC membranes deposited directly onto the transistor gate. Alongside the devices we developed the underlying theory, publishing a description of ionophore-doped membranes with a blocked interface that explains how these sensors respond over time.
Metal-Organic Frameworks Against Sensor Drift
The main obstacle to long-term potentiometric sensing is drift at the solid contact, where ionic signal must be converted into an electronic signal. We introduced metal-organic frameworks (MOFs) as ion-to-electron transducers for this interface, first in a highly stable lithium-selective electrode and more recently using conductive MOFs designed specifically to suppress drift. This work has been translated into a portable multiplexed ion-selective sensor for continuous, long-term monitoring of irrigation water quality, allowing growers to track nutrient and salinity levels in situ rather than sending samples to a laboratory.
Angstrom-Engineered Membranes for Lithium
Demand for lithium is expected to outstrip supply, making its selective recovery from brines and seawater a strategic priority. Because lithium, sodium and potassium ions are almost indistinguishable in size and charge, separating them requires control of channel chemistry and geometry at the angstrom scale. We have built such channels in graphene oxide nanosheets loaded with natural lithium-ion trappers, in MXene membranes tuned through their interlayer d-spacing, and in carboxylate-functionalised UiO-66 films with programmable ionic pathways. Our asymmetric MOF-on-MOF design, in which a bilayer structure narrows from 6 to 3.4 angstroms, produced an ionic current rectification ratio above 100 and selectivity ratios of 84 for K⁺/Li⁺ and 80 for Na⁺/Li⁺, among the highest reported for monovalent ion separation.
From Selectivity to Energy
The same nanochannels that separate ions can also generate power. Where a river meets the sea, the salinity gradient stores a large amount of recoverable energy, and a membrane that passes one ion while blocking its counter-ion converts that gradient into electricity. Our bioinspired heterogeneous MOF-on-MOF membrane delivered an output power density of 40.01 W/m² under a 500-fold concentration gradient and 9.20 W/m² with real sea and river water. We are extending this work with amphoteric zirconium-based MOF membranes and chelating-resin-modified polymers for sustainable osmotic energy generation.
Biosensing and Clinical Chemistry
Chemical sensing also has a place inside the body. We recently developed a miniaturised electrochemical biosensor for real-time in vivo monitoring of potassium in the inner ear, where ionic composition is tightly linked to hearing and balance function. Related projects include ZIF-8 photonic crystal biosensors for blood component recognition, MOF-based enzymatic microfluidic biosensors created by surface patterning and biomineralisation, and fluorescent carbon nanospheres for mercury detection in contaminated water.
Cleaner Water and Faster Discovery
Complementing the sensors, we develop low-cost natural clay and ceramic membranes for treating dye effluent, mine washery waste and aquaculture wastewater, and nanomembranes for capturing hazardous cations. Across all of these projects, we increasingly use machine learning to accelerate the discovery of ion-selective materials, an approach summarised in our edited volume Artificial Intelligence and Data Science in Environmental Sensing.
SELECTED PUBLICATIONS
Tonnah R.K. et al. Bioinspired and Engineered Ion-Selective Membranes Toward High-Flux and High-Selectivity Energy Devices. Small, 2026.
Arshadi F. et al. A Miniaturized Electrochemical Biosensor for Real-Time In Vivo Potassium Monitoring in the Inner Ear. Biosensors and Bioelectronics, 2026.
Esfandiari M. et al. Tackling Solid-Contact Sensor Drift Using Conductive Metal Organic Frameworks as Ion-to-Electron Transducers. Advanced Materials Technologies, 2026.
Abdollahzadeh M. et al. Portable multiplexed ion-selective sensor for long-term and continuous irrigation water quality monitoring. Computers and Electronics in Agriculture,
2024.
Tonnah R.K. et al. Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for Osmotic Energy Harvesting. ACS Nano, 2023.
Xiao H. et al. UiO-66-(COONa)2 membrane with programmable ionic channels for lithium ion-selective transport. Journal of Membrane Science, 2023.
Abdollahzadeh M. et al. Designing Angstrom-Scale Asymmetric MOF-on-MOF Cavities for High Monovalent Ion Selectivity. Advanced Materials, 2022.
Abdollahzadeh M. et al. Highly stable Li+ selective electrode with metal-organic framework as ion-to-electron transducer. Sensors and Actuators B: Chemical, 2022.
Asadnia M. et al. Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes. Analytica Chimica Acta, 2017.
Asadnia M. et al. Mercury (II) selective sensors based on AlGaN/GaN transistors. Analytica Chimica Acta, 2016.
Tonnah R.K. et al. Bioinspired and Engineered Ion-Selective Membranes Toward High-Flux and High-Selectivity Energy Devices. Small, 2026.
Arshadi F. et al. A Miniaturized Electrochemical Biosensor for Real-Time In Vivo Potassium Monitoring in the Inner Ear. Biosensors and Bioelectronics, 2026.
Esfandiari M. et al. Tackling Solid-Contact Sensor Drift Using Conductive Metal Organic Frameworks as Ion-to-Electron Transducers. Advanced Materials Technologies, 2026.
Abdollahzadeh M. et al. Portable multiplexed ion-selective sensor for long-term and continuous irrigation water quality monitoring. Computers and Electronics in Agriculture,
2024.
Tonnah R.K. et al. Bioinspired Angstrom-Scale Heterogeneous MOF-on-MOF Membrane for Osmotic Energy Harvesting. ACS Nano, 2023.
Xiao H. et al. UiO-66-(COONa)2 membrane with programmable ionic channels for lithium ion-selective transport. Journal of Membrane Science, 2023.
Abdollahzadeh M. et al. Designing Angstrom-Scale Asymmetric MOF-on-MOF Cavities for High Monovalent Ion Selectivity. Advanced Materials, 2022.
Abdollahzadeh M. et al. Highly stable Li+ selective electrode with metal-organic framework as ion-to-electron transducer. Sensors and Actuators B: Chemical, 2022.
Asadnia M. et al. Ca2+ detection utilising AlGaN/GaN transistors with ion-selective polymer membranes. Analytica Chimica Acta, 2017.
Asadnia M. et al. Mercury (II) selective sensors based on AlGaN/GaN transistors. Analytica Chimica Acta, 2016.