Vocab and Concepts for Biosensors

Biosensor

A device that combines a biological component, such as enzymes or antibodies, with a physicochemical transducer to detect and quantify specific biological analytes.

Example: Glucose sensor

Analyte

A substance whose presence are being selectively identified or measured by the bioresceptor

Bioprobe

a sensor that measures vital functions of living beings

Example: Blood pressure sensor

Immunosensors

A biosensor that measures immunological parameters

Transducer

converts one form of energy to another form of energy

In Biosensors, its typically electrochemical (chemical to electrical or electrical to electrical)

Biological elements in a biosensor

Enzymes, antibodies, nucleic acids, proteins, or bacteriophages

Biosensor as a general concept

consisting of two elements: a receptor and a detector

The receptor has to be biological material

Selectivity is at receptor not detector

Solid-State Sensor

operation of the device depends on effects an phenomena situated in a solid

Example: piezoresistive pressure sensor

Solid-state sensor does not imply a silicon-bases sensor

Integrated Sensor

Sensing function is integrated with the microelectronic component (directly influenced on an electrical component in silicon or other semiconductor materials)

Planar sensors

made using microelectronic production techniques, but semiconductor material characteristics are not material to the function of the sensor (On a surface no in surface)

Difference between Integrated vs Planar sensor

Integrated sensors are made IN silicon whereas planar sensor are made ON silicon

Smart sensor

A combination of interface electronics and an integrated or planar sensor on one chip

Advantages: Improves signal-to-noise and electromagnetic interference characteristics of the device.

Temperature compensation and calibration routines can be built into the sensing device itself

Electrochemical Sensors

a parameter the potential or conductance between two electrodes or the current through a polarized electrode is measured

Examples: Conductometric, potentiometric, and voltammetric

Potentiometry

measures the potential at an electrode in a solution (No current is allowed to change)

Voltammetric

measures of the current-voltage relationship in an electrochemical cell consisting of electrodes in a solution

*Potential is applied to the sensor and a current proportional to the concentration

Amperometry

A special case of voltammetry where the potential is kept constant as a function of time

Conductometry

Measurement of the conductance between two electrodes in a solution

Uses a small AC potential with small amplitude to prevent polarization

Difference between Potentiometry, Voltammetry, and Conductometry

Conductometry deals with Bulk solutions

Potentiometry and Voltammetry deals with surface or the near vicinity of the electrode

Impedimetric

Monitors change in resistance and capacitance

Capacitive

monitor change in capacitance

Electrochemistry Sensor Quick Definition

Electrochemical sensor makes use of electrochemical reactions

Clark Cell

measures dissolved oxygen

Used a silver anode and a gold or platinum cathode covered with an oxygen permeable membrane

Electrochemical Cell has…

at least two electrodes and electrolyte

Electrodes

consist of metals or semiconductors. it is the medium or phase through which charge is transferred by electronic movement

electrolyte

is the medium or phase through which charge is transferred by the movement of ions. it is typically a liquid fused with salts or ionically conducting solids

Electrochemistry deals with…

the process that transport the charge across interface between the electrode phase and the electrolyte phase. This transport through the interface involves a change from ionic conduction to electronic conduction.

Working electrode

The electrode which the half-reaction occurs. This may also be termed the indicator electrode

Reference Electrode

an electrode for which the half-cell potential is constant. The current phase in this electrode

Standard Hydrogen Electrode (SHE)

An internationally accepted reference electrode often identified as SHE or NHE (Normal Hydrogen Electrode)

Measures the amount of H+ in the solution as time changes

What electrode is the anode

The electrode at which an oxidations current flow is the anode

What electrode is the cathode

The electrode at which a reduction current is generated is the cathode

Galvanic Cells

A reaction occurs spontaneously at the electrode when connected by a conductor

Aode has a negative potential

Electrolytic cell

occurs only by applying external voltage to the electrodes

Anode has a positive potential

Nernst equation

the equation for the potential half-cell

electrochemical thermodynamics is the derivation of this equation

Electrochemical Double Layer

a buildup of ions between the electrode and electrolyte and electrochemical double layer is built up

Helmholtz Double layer

All the charges of the ions are on the metallic electrode that is uniformly distributed along the surface with + and - charges on electrode (Modeled it by parallel Plates)

Gouy and Chapman Double Layer

Found the distribution of ions around the electrode however, the highest concentration is near the electrodes

Stern and Graham Double Layer

Characterized the ion reaction within the solution as well as the charge potential. This is also the one that is used to this day.

Voltammetric experiments need…

a current varies linearly with concentration

Low drift in a sensor and residual current is essential

Linear dependence of the concentration on the current its more accurate

Poteniostat

a voltage source that is able to vary its otput potential in response to changes in the resistance across a circuit

Like an OpAmp