Biosensor Technology-a Game Changer

Biosensors are new, highly innovative devices used for detecting biological responses, which are converted into measurable data.

How Biosensors Work:

Biosensors capture biological data, which is first analyzed using algorithms and then translated into measurable quantity.

Advantages of Biosensors:

  • Detects & Prevents Progression of Illness
    Research has shown that biosensors highly effective in diagnosing the early onset of diseases caused by various infections. This technology has the ability to be used daily, as the sensors can be incorporated to mobile devices, which can synchronize personalized data to applications, which aids in remotely monitoring health. This data can be immediately available to physicians, which allows treatment to be more convenient and efficient. Early detection of these diseases can allow treatment to begin promptly, which increases the likely-hood of recovery.
  • Detects Blood-Alcohol Levels in the Body
    A recently designed wearable device called “Biosensor Tattoo” can sense the changes in the electric currents flowing through the sweat of the user. These changes in the electric currents determine blood-alcohol levels in the body. This information is then sent to the user’s mobile phone to alert them. This will allow users to make informed decisions as to whether it is safe to drive.
  • Detects Blood-Glucose Levels in the Body
    The advancement in biosensor technology allows diabetics to monitor their glucose levels in a more affordable, convenient way. This non-invasive device eliminates the use of multiple test strips.
  • Biosensor Technology can have a Huge Impact 
    Biosensor technology currently has a huge impact on the healthcare industry, but with time and innovation these sensors can revolutionize the way diseases are diagnosed. Biosensors play an important role when it comes to monitoring health.

Future of Plasmonic Biosensors

Introduction

Biosensors represent the technological side of the living senses that have found a routine application in amperometry enzyme electrodes for the decentralization of blood glucose measurement, for the interaction analysis by surface plasmon resonance in drug development, and to some extent, DNA chips for enzyme polymorphisms and expression analysis. These technologies have already reached a highly advanced level and need only minor improvement now.

Fundamentals

In the field of optics, the phenomenon of surface plasmon resonance (SPR), is widely used as optical biosensors. This was established from studies that involved the excitation of the surface plasmons on the metallic surfaces, especially noble metals. In this process, the metallic surfaces are exposed to light, a photon is trapped near them and that prompts electrons to move as a single entity. The oscillation of electrons on the metal film results in the formation of an electromagnetic field that decays out on the surface and is also known as the evanescent field.

Potential Applications

Point of Care

  • One of the primary applications of the biosensors is the development of the point- of-care testing system for prompt and precise therapy. This can be achieved by the integration of technologies such as disposable chips, portable platforms, miniaturization of the analytical machines and so on.
  • A smartphone-integrated analytical system can be used, which enables rapid diagnoses by allowing the data collected on the smartphone to be connected to medical doctors and institutions via Wi-Fi. In addition to this, disposable chips have also been developed as convenient devices with a simple operation such as color-change detection. Thus, the SPR sensors (e.g. immunosensor, etc.) have a great potential to utilize measurement of bio-markers due to their label-free, cost-effective analysis, and with the rapid response time. Because of these advantages, SPR-based sensors can facilitate high throughput and multiplex measurement of biomarkers when integrated with the microfluidic system.

SPR and Sensitivity

One of the challenges of the existing surface plasmon resonance (SPR) based sensors is that the sensitivity (if you would like to learn more about the biosensor sensitivity, click here) is not high enough for the measurement of biomarkers in small volumes of body fluids. Also, it is not a natural color change-based method, except for that of Au nano-particles.

Several efforts have been made to improve the sensitivity of the biosensors. These include metal surfaces, magnetic activity, grating or photonic crystals, etc. Meanwhile, the plasmonic effect which stimulates the SPR phenomena, can also stimulate another phenomenon that can also be applied to the development of immuno-sensors, including surface-enhanced Raman scattering (SERS), fluorescence resonance energy transfer (FERT), and metal-enhanced fluorescence) (MEF). If the SERS, FRET, MEF based analytical methods could be assimilated with an SPR-based sensor that employs plasmonic effects, targets can be measured in a better way and the drawbacks of each analytical method can be supplemented.

MOSPR and Sensitivity

  • Several plasmonic-based analytical methods have advantages with nano-structures and noble metals, and there is a possibility to develop a magneto-optic SPR sensor with high performance using an integrated platform.
  • Significant potential exists to develop MOSPR-based sensors with noble metals and nanostructures, for improvement in functionality as effective biosensors. The best advantage of this analytical method is in-situ, label-free detection. This could result in the development of several new types of sensors that can measure targets in a simple, rapid and cost-effective manner.


Figure: A microfluidic channel incorporated biosensor, and optical excitation scheme.

Currently, there are signific shortcomings in SPR-based immuno-sensor systems which is a challenge for effective detection. However, now the integration of magneto-plasmonic-based sensing systems can offer a breakthrough for the development of effective MOSPR sensors, for early diagnosis and point of care testing of various diseases, which in turn can significantly improve pharmaceutical, biomedical and clinical applications.

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Gas Sensors in the Industry Setting

Background

Gas sensors are devices used to detect the presence of gases in an area. Such sensors can be used to detect a gas leak or other emissions and can help shut down the process automatically by interfering with a control system. This is done in many different ways, one way is by sounding an alarm, which warns the operator in the area and indicates the location of the gas leak. What makes gas sensors so significant, is that they can detect gases that are harmful to organic life, animals, and humans.

Gas sensors are used mostly to detect flammable, combustible and toxic gases, as well as oxygen depletion. These sensors can be found in locations such as oil rigs, to monitor the processes of manufacturing, and are used emerging technologies such as photovoltaics.

Gas leak detection is the process in which potentially hazardous gas leaks are identified by sensors, and an alarm is sent off to inform people of the danger.  Another way of detection is the visual identity that can be carried out by using a thermal camera.

Gas detectors are classified as per their mechanism of operation such as oxidation, semiconductors, photoionization, catalytic, infrared, etc. They are classified into many categories:

  • Portable gas detectors are used to monitor the atmosphere around us, they are usually worn on clothing, a belt or harness. Such detectors are mostly battery-driven and they transmit warnings through audible and visible signals, such as flashing lights and alarms.
  • Fixed types of gas detectors are used to detect one or more types of gases. Such detectors are mounted near the process area of a plant, in control rooms, or an area of interest, such as a bedroom of a residence. Normally, industrial sensors are installed on a mild steel structure that is rigid where continuous monitoring can be carried out.

Types of Gas Sensors

Electrochemical gas sensor: Electrochemical gas sensors allow the gases to diffuse through a porous membrane to an electrode where it is either reduced or chemically oxidized. The determination of the amount of current produced is measured by the amount of gas that is oxidized at the electrode which indicates the concentration of the gas. Some customization in electrochemical gas detectors has been done by manufacturers, by changing the porous barrier to allow the detection of the concentration range for a certain gas. Moreover, since the diffusion barrier is a mechanical/ physical barrier, the detector tends to be more reliable and stable over the durability of the sensor and hence require less maintenance than any other early detector technology.

Catalytic Bead Sensor: These sensors are commonly used to measure combustible gases that present an explosion hazard when concentration levels are in between the upper explosion limit (UEL) and the lower explosion level (EL). The reference and active beads containing platinum wire coils are located on opposite arms of a Wheatstone bridge circuit and heated electrically, up to a few hundred-degrees Celsius. A catalyst present in the active bead allows combustible compounds to oxidize, thereby enhancing the heating of the bead even further and changing its electrical resistance. The result of the voltage difference between the passive and active beads is proportional to the concentration of all combustible gases and vapours present. The sampled gas can enter the sensor through a sintered metal frit, that provides a barrier to prevent an explosion when the instrument is carried into an atmosphere containing combustible gas. Pellistors measure all combustible gases, but they are more sensitive to smaller molecules that diffuse through the sinter more rapidly. The measurable concentration ranges are from a few hundred ppm to a few volume percents. Such sensors are robust and inexpensive, but require some minimum percentage of oxygen in the atmosphere to get tested and they can be poisoned or inhibited by compounds such as mineral acids, silicones, chlorinated organic compounds, and sulphur compounds.

Photoionization Sensors: These detectors use a high-photon-energy UV lamp to ionize chemicals in the sample gas. If the ionization energy of the compound is below that of the lamp photons, an electron will be ejected, and the resulting current is proportional to the concentration of the compound. The broad range of compounds can be detected at levels that range from a few ppb to several thousand ppm. Some detectable compound classes in order of decreasing sensitivity include olefins, alkyl iodides and aromatics, amines, sulphur compounds, ketones, alkyl bromides, organic esters, aldehydes and alkanes, and organic acids. Photoionization detectors are beneficial because of their simplicity and excellent sensitivity. The major limitation with these detectors is that their measurements are not compound-specific. Photoionization detectors are widely used for industrial hygiene and environmental monitoring. They are usually bench-type, miniature, hand-held clothing clipped PIDs.

Infrared Point Sensors: These sensors use radiation which passes through the volume of gas. In these sensors, energy from the sensor beam is absorbed in certain wavelengths, depending on the properties of a specific gas. For example, carbon monoxide absorbs wavelengths of about 4.4-4.5 micrometers. The energy of this wavelength is compared to a wavelength outside of the absorption range. The difference in energy between these two wavelengths is proportional to the concentration of gas present. The advantages of these sensors that they do not have to be placed into the gas to detect it and can be used for remote sensing. The infra-red sensors are used for detecting hydrocarbons and other infrared active gases such as carbon dioxide and water vapour. These sensors are commonly found in refineries, waste-water treatments, chemical plants, gas turbines, chemical plants, and other facilities where flammable gases are present and there is a possibility of explosion. The remote sensing can monitor large volumes of space. Infrared sensors are also being researched in the area of Engine Emissions. The sensor detects high levels of carbon monoxide and other abnormal gases present in vehicle exhaust.

Infrared Image Sensors: These sensors include both active and passive systems. For active sensing, infrared imaging sensors usually scan a laser view of an entire scene and track for the backscattered light at the absorption line of the wavelength of a specific target gas. Passive imaging sensors, on the other hand, measure spectral changes in every pixel of an image and explore individual spectral signatures that indicate the presence of target gases. The compound types that can be imaged are similar to the ones that can be detected with infrared point detectors, but the images can help identify the source of gas.

Semiconductor Sensors: These sensors are known as metal-oxide-semiconductor sensors. They detect gases by a chemical reaction that takes place when the gas comes in direct contact with the sensor. The common material used in semiconductor sensors is tin oxide. The electrical resistance in the sensor reduces when it encounters the monitored gas. The change in the resistance is used to calculate the gas concentration. Semiconductor sensors are usually used to detect oxygen, hydrogen, alcohol vapour, and poisonous gases such as carbon monoxide. Semiconductor sensors are commonly used in carbon monoxide sensors and breathalyzers. Semiconductor sensors must encounter the gas to detect it and they work for a smaller distance as compared to ultrasonic and infrared point detectors. Semiconductor sensors can detect various gases such as sulphur dioxide, hydrogen sulphide, carbon monoxide, and ammonia. These sensors have been widely used since the 1990s.

Ultrasonic Non-gas Detectors: These are not gas detectors; they detect the aural emission created when a pressurized gas expands in a low-pressure area through a small outlet (point of leakage). These devices use aural sensors to detect the changes in the background noise of their environment. As high-pressure gas leaks generate sound in the ultrasonic range of 25 kHz to 10 MHz, the sensors can easily differentiate the frequencies from the background aural noise (which is 20 Hz – 20 kHz). The ultrasonic gas leak detectors cannot measure the concentration of gas, but they can determine the leak rate of gas escaping. This is because the ultrasonic sound level depends on both the pressure and size of the gas leak.

Ultrasonic gas detectors are mostly used for remote sensing in the outdoors where weather conditions can easily disintegrate evading gas even before it reaches the leak detectors that require interaction with the gas to detect it and sound an alarm. Ultrasonic detectors are commonly found on offshore and onshore oil/gas platforms, gas turbine power plants, gas compressors, metering stations, and other facilities that have outdoor pipelines.

Holographic Gas Sensors: These sensors use light reflection to detect changes in a polymer film matrix that contain a hologram. As holograms tend to reflect light at certain wavelengths, any change in their composition can generate a colorful reflection that indicates the presence of a gas molecule. Holographic sensors require sources of light such as a CCD detector or an observer, or white light or lasers.