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Module 1- Sensors and energy system
Sensor
A sensor is device that is capable of giving real time analytical information about the test sample. It interacts with specific chemical or biological analyte, detects it and produce the signal proportional to its quantity.
Main components of sensor
a) Receptor b) Transducer c) Actuator
Receptor: The receptor is the component of the chemical sensor that comes into direct contact with the analyte and produces non electrical signal proportional to its quantity.
Transducer :A transducer is a device that converts a non-electrical signal into an electrical signal. These are used to convert the signal created by the receptor-analyte interaction into a measurable value.
Actuator: Actuator would receive inputs from any system in the form of electrical signals and then generate an output for its environment. Here electrical signal is converted into mechanical work. It converts electrical energy into mechanical energy. For example, a fan is used to reduce temperature
Working principle and applications of an electrochemical sensor
Electrochemical sensors convert the information associated with electrochemical reactions (the reaction between an electrode and analyte) into measurable signal. Electrochemical sensors are made up of three essential components: a receptor that binds the sample, the sample or analyte, and a transducer to convert the chemical interactions into a measurable electrical signal. In electrochemical sensors, the surface of the electrode which is in contact with analyte acts as receptor because on this site of the electrode, electrochemical reactions takes place and produces non-electrical signal.
The electrode acts as the transducer because it will convert non-electrical signal produced by receptor into electrical signal. The role of the electrolyte is to transport charge within the
sensor, contact all electrodes effectively, solubilise the reactants and products for efficient transport, and be stable chemically and physically under all conditions of sensor operation. Electrochemical sensors require a closed circuit. Current must flow to make a measurement. The electrode will either oxidize or reduce the analyte producing non - electrical signals. The main steps involved in working of electrochemical sensors are
- Diffusion of the analyte/electrolyte interface (in the liquid phase)
- Adsorption on to the electrode surface
- Electrochemical reaction with electron transfer
- Desorption of the products
- Diffusion of the products away from the reaction zone to the bulk of electrolyte or gas phase.
Applications of electrochemical sensors:
- The electrochemical oxygen sensors is used for detection of dissolved oxygen in water, boiler and to monitor the dissolved oxygen concentration in metals, glasses and in hydrogen fuel.
- Electrochemical sensors are used in security and defence application like detection of toxic gas, warfare agents etc.
- Electrochemical sensors are used in water analysis to measure the toxic metal concentration in water.
- They are used in diagnostic and health care application like in situ monitoring of glucose serum , uric acid, blood Ca+2, Fe+2^ etc
Working, principle and applications of Conduct metric sensors
In conductometric sensor determination of the concentration of analyte is based on the measurement of changes in the electrolytic conductance of solution.
Conductance of the solution is based on
- Concentrations (number) of ions in the solutions
- Mobility of each type of ions in solution. Mobility of ions depends on its size. Smaller the size higher is the mobility and hence higher is the conductance.
An electrode used in conductometric sensor is called as conductivity cell. It is made of two platinum electrodes with unit cross sectional area and unit distance between them. Volume
Applications of thermometric sensor sensors:
- Thermal bio sensor are used in the determination of metabolite, bioprocess monitoring and environmental control.
- They are used for the determination of combustible gases react with oxygen at the surface of suitable catalyst
Working, principle and applications of Optical sensors (colorimetry)
Sensors based on measurement of interaction of electromagnetic radiation with the chemical species are called as optical sensor. In optical sensor, optical signal arises from the interaction of the analyte with incident radiation. Interaction could result in absorption, emission, scattering or reflection of light. The type of interaction depends on the wavelength of the probing radiation and on the structure of the molecules in the analyte. Intensity of radiation emitted from the analyte carries information on the concentration of the analyte Simple optical sensor used to measure absorption of light. Main components are light source, wavelength selector, photo detector and display. Optical sensors are used to determine concentration of coloured species in the solution. They are based on the measurement of absorbance or transmittance of light of particular wavelength by the coloured species in the solution. They obey Beer-lamberts law
Applications of Optical sensors
- Optical Fibre based biosensors are used in detection of explosive.
- These are used in smart watches to measure the heartbeat of the person.
- Water and liquid levels in industries.
- Adjusting screen brightness in smart phone
Electrochemical sensors for the measurement of dissolved oxygen (DO).
Oxygen present in water is called dissolved oxygen (DO).
- In an electrochemical DO sensor, 2 electrodes used are of dissimilar metals.
- Zinc or lead is used as anode and silver metal is used as inert cathode
- The difference in potential between anode and cathode should be more than 0.5V to reduce dissolved oxygen without an external applied potential
- The electrolytic solution used is sodium chloride or any other inert electrolyte.
- When electrode are dipped in water to measure its DO, anode ubdergoes oxidatiob liberating electrons 2 Z n 2 Z n+2^ + 4 e-
- At cathode DO undergoes reduction. Ag cathode is inert; it passes electrons to oxygen for reduction.
- O 2 + 2 H 2 O+ 4 e-^ 4 OH- Over all reaction 2 Z n + O 2 + 2 H 2 O 2 Zn(OH) 2 The current produced by the reduction oxygen at the cathode is proportional to the partial pressure of oxygen in the water sample. Zinc hydroxide (Zn (OH) 2 ) that is produced is precipitated out into the electrolyte solution. This will affect the sensor performance. when sensor reading are not stable, then electrolyte and zinc anode have to replaced to bring the sensor back to working condition
Electrochemical sensors for the pharmaceuticals taking diclofenac as an
example
Diclofenac is one of the most frequently prescribed non-steroidal, anti-inflammatory drugs with antipyretic and analgesic effect. Its chemical name 2 - (2-(2,6-dichloroanilino) phenyl)acetic acid. It is safe in prescribe dose but may cause adverse effects at higher dose. Electrochemical sensor can be used to detect diclofenac in lower concentration. These sensors are fast, low cost, and sensitive. These sensors can be used for on the spot analysis. In the electrochemical sensor used to detect diclofenac, the sensing (working) electrode is graphite carbon coated with multi walled carbon nano tubes (MWCNT) and gold nano particle s. In the detection, along with sensing electrode, counter electrode and reference electrodes are used. When the sample containing diclofenac is put in the sensor, the following
OH
1-Hydroxypyrene
O O
Electrochemical gas sensors for SOx and NOx
Electrochemical sensors are used to measure the concentration of pollutant gases like NO 2 , NO and SO 2. A filter is used to prevent unwanted contaminants. An electrochemical gas sensor generally consists of a sensing electrode, counter and reference electrode along with a gas-permeable membrane. The gas-permeable membrane allows only the gas not liquid. During sensing operations, it is submerged in an electrolyte.. An electrochemical reaction either oxidation or reduction, depending on the type of gas occurs when the gas reaches the working electrode or sensing electrode. An oxidation reaction moves electrons from the working electrode to the counter electrode, while a reduction reaction causes electrons to move from the counter electrode to the working electrode. In either case, the electrical current generated is proportional to the concentration of the target gas. The current is then amplified and processed to give the user a reading in either parts per million (PPM) or percentage volume.
Detection of NO 2 Detection of NO 2 in an amperometric gas sensor in aqueous electrolyte is based on the following electrochemical reduction reaction on the surface of sensing electrode. Au, Pt/Nafion is used as sensing electrode with 10 M H 2 SO 4 as an electrolyte. NO 2 + 2H+^ + 2e-^ NO + H 2 O
Detection of NO Detection of NO an amperometric gas sensor in aqueous electrolyte is based on the following electrochemical oxiadtion reaction on the surface of sensing electrode. Au /NASICON- NaNO 2 is used as sensing electrode and electrolyte. NO + 2 H 2 O NO 3 -^ + 4H+^ + 3e-
Detection of SO 2 Detection of SO2 in an amperometric gas sensor in aqueous electrolyte is based on the following electrochemical oxiadtion reaction on the surface of sensing electrode. Au /Nafion is used as sensing electrode with 0.5 M H 2 SO 4 as an electrolyte. SO 2 + 2 H 2 O SO 42 -^ + 4H+^ + 2e-
Disposable sensors
Portable sensor used for on-the – spot analysis using disposable strip with receptor and electrode printed on it, is called disposable sensor. These strips can be inserted into the portable system and used for on-site sample analysis.
Disposable sensors in the detection of bio molecules taking example
ascorbic acid (vitamin-C )
Disposable pre activated screen printing electrodes have been developed for spot analysis of ascorbic acid (vitamin-C).
In the disposable strip, active materials of the sensing electrode, counter electrode and reference electrode are printed on the disposable paper strip using screen printing technology. Active material coating on sensing electrode must be capable of oxidising ascorbic acid on its surface. The ascorbate oxidase enzyme immobilised on a screen printed carbon electrode is used as sensing electrode. It oxidizes ascorbic acid into dehydroascorbic acid. Concentration of ascorbic acid is determined from the change in potential of the oxidation process.
Energy Systems:
Battery:
It is a device that consists of one or more cells connected in series or parallel and used to store and generate power and acts as portable source of electrical energy.
Construction, working and applications of Lithium ion battery
Anode - Lithium intercalated in graphite as anode (Li/C) Cathode – Lithium Cobalt Oxide (LiCoO 2 ) or Lithium manganese oxide (LiMnO 2 ) or metal oxide
Electrolyte – Lithium salt such as LiPF 6 in organic electrolyte mixture (such as ethylene carbonate – dimethyl carbonate) Separator – Polypropylene.
Electrode reactions: While discharging, lithium atoms present in the graphite layer are oxidized, liberating electrons and lithium ions. Electrons flow through external circuit to the cathode and lithium ion moves through the electrolyte towards cathode. At cathode lithium ions are reduced to lithium atoms and are inserted into the layered structure of metal oxide.
xLiC 6 xC 6 + xe-^ + xLi+
At anode
At cathode Li1-xCoO 2 + xLi+^ + xe-^ LiCoO 2
When the cell is charging, the reverse occurs. Lithium present in the layered metal oxide oxidizes, liberating electrons and lithium ions. Electrons flow through external circuit and lithium ion moves through the electrolyte towards anode.
At cathode LiCoO 2 Li 1 - X CoO 2 + xLi+^ + xe- At anode xLi+^ + xe-^ + xC 6 xLiC 6
Applications : Used in mobile phones and smart phones, laptops and tablets, digital cameras and camcorders, electronic cigarettes, handheld game consoles and torches (flashlights). Li-ion batteries are used in tools such as cordless drills, sanders, saws and a variety of garden equipment including whipper- snippers and hedge trimmers.
Construction, working and applications of Lithium ion battery Sodium –
ion battery (Na- ion Battery)
Anode – Hard carbon/ Na Cathode – Sodium inserted layered metal oxide,(NaMO 2 ) Electrolyte – NaPF 6 dissolved in organic solvent mixture (such as ethylene carbonate- dimethyl carbonate) The Separator – Polypropylene.
Aluminum is used as current collector.
conversion of solar energy into electrical energy is very high compared to conventional solar cell.It is used to replace bulky materials such as silicon or gallium selenide.PbS(lead sulphide), PbSe, CdSe, CdSare commonly used quantum dots. Construction A QDSSCs consist of three components: a) Photoanode b)Cathode c) Electrolyte a) Photo anode: It is the working electrode in the cell. It is a conducting glass, over which a large band gap semiconductor like TiO 2 is coated.This is further coated with Quantum dots(QD’s) such as PbS(lead sulphide),PbSe, CdSe, CdS which acts as photosensitizer. b) Electrolyte: An electrolyte such as Polysulphideis placed between anode and cathode with also acts as separator. c) Cathode: Cathode is made up of inert metalwhich is used to complete the circuit.
Working
- QD’s present on photo anode is exposed to sunlight.
- QD’s absorb solar energy and get exicited,i.e electrons jump from valence band to conduction band producing electron hole pairs. QDs + hγ QDs* QDs* e-^ + h+
- The electrons from QDs are transferred to the conduction band of wide band gap TiO 2 semiconductor, leaving holes on the surface of QD’s.
- Electrolyte takes up holes from the surface of QD’s and gets oxidised. S^2 -^ + 2h+^ S
- Electrons flow from photo anode to cathode through external circuit generating an electric current.
- At, cathode electrolyte is regenerated taking up electrons from the cathode. S + 2e-^ S^2 -
Quantum dots solar cell applications
It is used a slight-emitting Diodes
It is used as Photo conductors and photo detectors
It is used in Drug delivery.
Biosensors
