Chapter 1. Introduction to Sensors and Biosensors
Classification of sensors
- Physical sensor: a sensor is a device that detects or measures a physical property and records,
indicates or otherwise responds to it (Oxford English Dictionary), e.g., pressure and distance sensors.
- Chemical sensor or chemisensor: a device which responds to a particular analyte in a selective way
through a chemical reaction and which can be used for the quantitative or qualitative determination
of the analyte, e.g., pH electrode, oxygen electrode.
- Biological sensors or biosensors:
• “self-contained integrated devices which are capable of providing specific quantitative or semi-
quantitative analytical information using a biological recognition element (biochemical receptor)
which is in direct spatial contact with a transducer element”.
• “compact analytical devices incorporating a biological or biologically derived sensing element
either integrated within or intimately associated with a physicochemical transducer. The usual aim
of a biosensor is to produce either discrete or continuous digital electronic signals which are
proportional to a single analyte or a related group of analytes”.
Biosensors are a subset of chemical sensors, should be distinguished from a bioanalytical system, which
requires additional processing steps, such as reagent addition and also from a bioprobe which is either
disposable after one measurement or unable to continuously monitor the analyte concentration. Biosensors
that include transducers based on integrated circuits are known as biochips.
Principle of (bio)sensors
Analyte or physical quantity
- Physical quantity: pressure, acceleration, velocity, movement, relative humidity, temperature,
distance, radiation, vibration, resistance…
- Chemical analyte: pH, O2, CO2, ammonia, toxic gasses, ions, glucose, amines, toxins, bacteria...
Biological detection or bio-recognition element
The key components of any biosensor device: enzymes, antigens-antibodies (IgG), nucleic acids, cellular
structures (mitochondria), whole cells (bacteria, yeast, fungi, eukaryotic), plant or animal tissue slices (liver,
skin), biomimetic/synthetic receptors… And the immobilization to the transducer by adsorption, entrapment
or encapsulation.
Transducer
It is a device that converts an observed change (physical or chemical) into a measurable signal and can be:
- Electrochemical: amperometric (voltammetric), potentiometric, conductometric…
- Mass sensitive: piezo-electric devices, surface acoustic waves…
- Optical transducers: absorbance, reflectance, luminescence, refractive index, light scattering…
- Thermal sensors: thermistor, pyroelectric, optical enthalpimeter, calorimeter…
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,Actuator
It puts into action by display (LCD, needle...) and activates another system (e.g.valve system).
Data acquisition
Can be done either by hardware or software and the signal processing by filtering. Data is analysed by
statistical process control, univariate statistics (ANOVA, regression...) and multivariate statistics
(chemometrics).
Interdisciplinary research
Sensor performance factors
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, Areas of application
- Health care and diagnostic medicine: cancer biomarkers (PSA...), blood gases and ions, glucose
(diabetes), lactate (acidification of muscles), hormones (pregnancy test), urea (urine), cholesterol, viral
detection (Hepatitis B, Influenza A...), microbiological assays (infectious diseases ...)
- Agriculture and biological production chain: traceability (RFID), food quality (taste, aroma, colour, ...),
food safety (BSE, dioxin, bird plague, adulterants, pathogens (Salmonella, Campylobacter, E. coli
strains), toxins (botulism), food allergens(nuts)), functional foods
- Warfare, bioterrorism and space technology: anthrax, poisonous gas detection…
- Environmental monitoring: water monitoring (biochemical oxygen demand, acidity, salinity,
phosphate, nitrate, pesticides, fertilizers, endocrine disruptors (oestrogens and oestrogenic mimics),
caffeine, air monitoring (air pollution), soil monitoring…
- Control of industrial processes: off-line in laboratory or on-line in real time, food and beverage
industry, fermentation processes…
Relation to nanotechnology
There is no widely accepted definition of nanotechnology, all definitions refer to the scale of the technology,
nanotechnology works at the nanoscale (10-9 m).
- “Areas of technology where dimensions and tolerances in the range of 0.1 nm to 100 nm play a critical
role” www.nanoforum.org
- “Nanotechnology cannot be defined in terms of dimensions alone. In fact, it represents a convergence
of the traditional disciplines of physics, chemistry and biology at a common research frontier” P.
Busquin, Former European Commissioner for Research.
There is a convergence of both approaches:
- Top-down approach: the nanoscale is reached by miniaturization in mechanics and electronics (MEMS
to NEMS).
- Bottom-up approach: processes at the nanoscale are studied and result in new phenomena,
technologies and products: quantum dots, scanning probe microscopes, direct manipulation of atoms:
“shaping the world atom by atom”, supramolecular self-assembly, quantum physics, chemistry and
biology.
There are some health issues regarding nanomaterials such as implications of nanoparticles and
nanomaterials on human health and environment. E.g. titanium dioxide particles in sun screen and cosmetics.
Nano-electronics of embedded computers resulted from an ever-increasing calculation power per surface
area computer chip like:
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