## 5 Lacase-Based Sensor Development
Another fiber-optic-based lactose biosensor for polyphenic compound detection has been developed by [PERSON] et al. [142]. They used lactose from _Pleorotus oostreatus_ that was immobilized on the surface of a commercially available fiber optic oxygen sensor. Tetramethyl orthosilicate (TMOS), trimethoxymethylsilane (Tri-MOS), and polyvinyl alcohol (PVA) were added to the immobilized lactose region as a diffusion layer. In Figure 21, the sensing mechanism is shown. The detection mechanism exploits the luminescence emission from oxygen-sensitive dyes contained in sensing spots. After excitation, the interaction between the luminescent dyes and an oxygen molecule causes the transfer of the excess energy to that molecule,  
Figure 21: Sensing scheme of the oxygen-detection-based optic system (reproduced from Ref. [142] under open access conditions). Figure 20: Sensing scheme for detection of polyphenols based on “turn-off” photoluminescence using enzyme immobilized CdTe QDs (reproduced with permission from Ref. [140]). exploiting a dynamic quenching process (Figure 21). The light emission intensity from sensing spots and the average excitation lifetime decreased. The excitation lifetime and oxygen concentration are related by the Stern-Volmer relationship, and the phase modulation technique is applied for precise measurements [143]. The sensor spot is excited with sinusoidally modulated light, and the emitted light is also sinusoidally modulated. The average excitation lifetime is then detected as the phase angle between these two optical signals. The measurements are carried out in a flow-through system. The [PERSON] et al. [142] biosensor is characterized by a large linear range for catechol (40-600 uM), as shown in Figure 22. The other working parameters are reported in Figure 16:0 In agreement with the authors, the designed biosensor can be easily produced and is reproducible and stable. The authors propose its use in the food industry as well as in environmental monitoring for the detection of phenolic compounds. Well-known optical biosensors are characterized by high sensitivity and offer significative advantages in terms of sensitivity, linear range and LOD. They are also chemically inert, effective for remote sensing, and immune to electromagnetic interference. Also, lactose-based biosensors profit from these advantages, but some of them can suffer from the low specificity that characterizes this enzyme [3; 144; 145]. However, some immobilization procedures or other strategies can be adopted to obtain an increase in the specificity towards phenolic substrate [8; 146]. In order to compare the performances of the different biosensors described above, we reported their main working parameters in Table 3, which provides an overview of different approaches for the detection of phenolic compounds through the development of spectrophotometric and fluorescence sensors for environmental and food applications. This table reports information concerning the main biosensors' working parameters, including the following: sensitivity, linearity range, limit of detection (LOD) and response time. The optical absorption-based approach constitutes the preferential choice of allowing an LOD of a few uM with a response time equal to a couple of minutes. Concerning florescence-based biosensors, they show comparable performances; that said, in recent years, the use of nanotechnologies has allowed the design and fabrication of highly performing optical biosensors [140; 141]. The optical methods shown in Table 3 are among the most widely used, but more innovative techniques, such as those based on SERS, are emerging. In recent years, great interest has been shown in the development of nanozymes that mimic natural enzymes. The development of these nanomaterials permits overcoming the drawbacks that characterize natural enzymes such as a high price, poor stability, and difficulty to recycle. Nanozymes can have a low price, high stability, and tailored activity.