The superscript E indicates a constant electric field (which corresponds for example to a short circuit condition, where E=0), as well as the superscript S stands for a condition of constant strain.For each couple of constitutive equations there is a different piezoelectric coefficient, defined as:eip?(��Di��Sp)E=?(��Tp��Ei)Sdip?(��Di��Tp)E=(��Sp��Ei)Tgip??(��Ei��Tp)D=(��Sp��Di)Thip??(��Ei��Sp)D=?(��Tp��Di)S(2)Related to each other as follows:dip=?ikTgkpeip=diqcqpEgip=dkp/?ikThip=giqcqpD(3)An important parameter is the electromechanical coupling factor, kiq, which describes the conversion between mechanical and electrical energy.

It can be written in terms of coefficients of the material:kiq2?Wi(electrical)Wq(mechanical)=eiq2?ikTcpqE=eiq2?ikScpqE+eiq2(4)The efficiency of energy conversion, ��, is described, at resonance, as follows:��=k22(1?k2)1Q+k22(1?k2)(5)where, k2 is the coupling factor as defined in Equation (4) and Q is the quality factor of the generator [21,27].To understand how the electrical quantities (V and I) are related to the mechanical ones (force F and displacement z), the particular case of a piezoelectric disk can be considered. In this case, from Equation (1) the following relationships can be obtained [28]:{FP=kPEz+��VIp=��z�B?CpdVdt(6)In which the featuring quantities are the restoring force Fp of the piezoelectric material, its stiffness when it is short-circuited kPE, the displacement z, the force factor ��, the voltage across the electrodes V and the outgoing current Ip, and the clamped capacitance Cp.

These equations are derived considering the following approximations:E=?VH;S=zH;Ip=AdDdt;FP=ATp(7)and the featured quantities can be written as:kPE=cpqEAH;Cp=?ikSAH;��=eiqAH(8)where, A and H are the section and thickness of the piezoelectric disk.In a more generic case of a mechanical stress in direction p and an induced electric field in direction i, the open-circuit voltage of a piezoelectric device can be written as follows:V=Tpgipl(9)Assuming that the voltage coefficient gip is constant with the stress, and where l is the gap between the electrodes.3.?MaterialsEach piezoelectric material can be characterized with a set of parameters. For example, considering a stress Tp as input, the strain coefficient dip gives the relationship between the applied stress and the electric induction Di (therefore, current density is Jp=dDdt), while the voltage coefficient gip gives the voltage Equation (9).

Thus, a high energy density piezoelectric material is characterized by a large product of the strain coefficient (dip) and the voltage constant (gip) [29]. The coupling factor kiq, combining the piezoelectric properties of the material with its mechanical and electrical properties, gives the converted Drug_discovery energy and efficiency of the harvester, as remarked by Equations (4) and (5).

Hence, sensory evaluations have several problems, for example, low objectivity, low reproducibility, the stress possibly imposed on panelists and the significant cost of selecting and training panelists. Additionally, in the medical and pharmaceutical industries, it is difficult to carry out sensory evaluations because of the potential for medication side effects. Although quantitative analysis can be conducted, it cannot be used to estimate the intensities of each basic taste. Against these backgrounds, objective methods of evaluating tastes without using human sensory systems have attracted attention. The development of objective methods of evaluating taste should contribute greatly to the compliance of drug products and the qualities of foods and beverages.

Examinations of objective methods of taste evaluation, such as electronic tongues (e-tongues), have been performed worldwide [16�C23]. Since e-tongues are potentiometric multisensor systems mostly using metal and ion-selective electrodes, principal component analysis (PCA) and partial least squares (PLS) analysis are generally carried out to analyze taste information obtained by sensor outputs with low selectivity. Objective evaluations of the taste of unknown samples are difficult, because PCA needs to define the meanings of each principal component. In spite of this issue, e-tongues are suitable for comparing and distinguishing known samples, such as for quality control. There have been reports on the assessment of the bitterness of drugs and bitterness-masking formulations using e-tongues [16,18,20,23].

Rundnitskaya et al. [23] mentioned the quantification of bitterness of structurally various active pharmaceutical ingredients using an e-tongue under parameter-limited conditions.Our research team has developed a taste sensor, which is an e-tongue with global selectivity, using some electrodes with lipid/polymer membranes comprising a lipid, polyvinyl chloride (PVC), and a plasticizer as sensing parts [24�C29]. Global selectivity is one of the unique characteristics of our taste sensor. This means that the taste sensor must respond consistently to the same taste similarly to the human tongue, despite Drug_discovery the various chemical structures and sizes of tastants. The taste sensor has been commercialized by Intelligent Sensor Technology, Inc., (Kanagawa, Japan) as a taste sensing system and is the first e-tongue system commercialized in the world.

Each taste sensor electrode in the sensor system has global selectivity, responding to only one taste. The taste-sensing system is a potentiometric measurement system, which determines the membrane potential of lipid/polymer membranes. The change in membrane potential is used as the sensor output. It is caused by electrical and hydrophobic interactions between the lipid/polymer membrane and tastants in a sample solution.

Different methods have been developed till now for the synthesis and protection of the gold nanoparticles apart from the classical methods [24-26], using tryptophan [27], amines [28-29] cinnamic acid [30], polypeptides stabilized [31-32], ethylene glycol protected [33], glutathione [34], lipoic acid-Poly (�é\benzyl�\L�\glutamate) [35].The capped gold nanoparticles are used for coupling of biomolecules, and a suitable enzyme, which can be used for this coupling is horseradish peroxidase (HRP). HRP has been used for the detection purpose because of the small size and high stability to the chemical modifications. Peroxidases are enzymes of the EC 1.11.X.X class, which are defined as oxidoreductases that use hydroperoxides as electron acceptor.

It has been found that peroxidases such as plant peroxidases, cytochrome c peroxidase, chloroperoxidase, lactoperoxidase etc, are heme proteins with a common catalytic cycle [36] (Scheme 1). HRP is a globular glycoprotein with a mass of 42 kDa, of which the protein moiety is approximately 34 kDa, the rest of the molecular weight being accounted for by the prosthetic group (b-type heme), two calcium ions and some surface bound glycans.Scheme 1.The reactions in the enzymatic catalytic cycle of HRPThe first reaction (1a) involves the two-electron oxidation of the ferriheme prosthetic group of the native peroxidase by H2O2 (or organic hydroperoxides). This reaction results in the formation of an intermediate, compound-I (oxidation state +5), Brefeldin_A consisting of oxyferryl iron (Fe (IV) 0=O) and a porphyrin �� cation radical.

In the next reaction (1b), compound-I loses one oxidizing equivalent upon one-electron reduction by the first electron donor AH2 and forms compound-II (oxidation state +4). The later in turn accepts an additional electron from the second donor molecule AH2 in the third step (lc), whereby the enzyme is returned to its native resting state, ferriperoxidase.Direct electrochemistry has been observed for the adsorbed peroxidase. There was a registered reduction in the current and peroxide concentration that was observed in gold [37], graphite [38-39] and platinum [40]. The electrode current was found due to an electrochemical reduction of compound�\I and compound�\II as schematically presented in Figure 1 below. In this work, we have explored the electrochemistry of covalently coupled enzyme.Figure 1.Mechanism of the direct bioelectrocatalytic reduction of hydrogen peroxidase at peroxidase-modified electrodes. P+ is a cation radical localized on the porphyrin ring or polypeptide chain.