**2. Electrochemical signal transduction techniques**

A transduction process involves efficient capture of biological or chemical recognition signals and their conversion into electrical, gravimetric, optical, electrochemical or acoustic signals. There are four main types of electrochemical signal transduction techniques that can be used in analysis, depending on the reaction under investigation:

i.Voltammetry

ii.Potentiometry

iii.Amperometry

iv.Conductometry

Each of these techniques is described in the following section in brief.

### **2.1 Voltammetry**

Voltammetry is an electroanalytical method that obtains information about an analyte by modifying a potential and then measuring the resultant current. Here, the potential sweep is applied between working electrode (WE) and counter electrode (CE) with respect to reference electrode (RE), and the current so produced is measured as an analytical signal. Because the potential can be varied in many ways, many forms of voltammetry are available, such as direct current (DC) polarography, differential pulse polarography (DPP), differential staircase voltammetry, cyclic

*An Overview of the Synergy of Electrochemistry and Nanotechnology for Advancements… DOI: http://dx.doi.org/10.5772/intechopen.106151*

voltammetry, linear sweep voltammetry, normal pulse, and reverse pulse voltammetry [8–10]. Cyclic voltammetry is one of the most widely used electroanalytical methods.

#### **2.2 Potentiometry**

In potentiometry, the analytical signal is the open-circuit voltage between working electrode and reference electrode. Depending on the concentration of the analyte, this signal can increase or decrease [11]. Here, Nernst equation governs the relationship between concentration and potential. Useful information about ion activity in redox reaction is provided by potentiometry [12]. Ion-selective electrodes (ISEs) are often employed to achieve low detection limits for potentiometric sensors. Also the potentiometric sensors are ideal for measuring low concentrations of analyte in small sample volumes, because they do not chemically influence the sample [13].

#### **2.3 Amperometry**

It is similar to voltammetry with the difference that here a constant or stepped potential is employed to measure the current as electric signal, whereas in voltammetry, controlled variation of voltage is done to measure current. In fact, some scientists classify voltammetry as a type of amperometry only, because both these techniques employ measurement of current upon variation of potential. Here, a continuous measurement of current is done, and this current is produced by oxidation or reduction of an analyte in a biochemical reaction [9, 14]. Here, the peak value of the measured current (over a linear range of potential) is a direct indication of the bulk concentration of the electroactive species [15, 16]. Glucose biosensor is one of the most widely employed amperometric sensors. It is often claimed by many scientific practitioners that amperometric sensors are superior to potentiometric sensors when it comes to sensitivity [17].

#### **2.4 Conductometry**

Conductometry sensors are used to measure concentrations of electrolyte in aqueous solutions. The recorded electrical resistance of the solution is used to calculate the molar concentration of an identified electrolyte that causes solution conductivity [18]. Conductivity can be measured directly with a conductivity metre or indirectly with conductometric titration. Electrolyte conductometric analysis has long been used. Conductometric methods were used to analyse mineral waters and salt solutions by Henry Cavendish and Andreas Baumgartner [19].

## **3. Types of sensors**

Sensors can be classified into two broad categories depending on their application or mode of transduction, as follows:

#### **3.1 Types of sensors on the basis of application**

i.**Chemical Sensors:** A chemical sensor converts an analyte's physical and/ or chemical properties into a measurable signal [20]. The intensity of the measurable signal is normally proportional to concentration of the analyte [21]. The chemical sensors can further be classified as follows:

