## 1 Introduction  
Phenolic compounds, natural compounds found mostly in fruits and vegetables, are secondary plant metabolites and contribute to the oxidative stability of biological systems as compounds with antioxidant properties [1; 2; 3]. For this reason, they are the subject of numerous scientific research studies on their beneficial effects on human health [3]. One important compound is caffeic acid (3,4-dihydroxycinnamic acid), which belongs to the class of phenolic acids, one of the main classes of phenolic compounds. It is found in high levels in coffee, green tea, olive oil, and wine, and it is known for its antioxidant activity due to its chemical structure (phenolic groups in positions 3 and 4), which allows the transfer of electrons and hydrogen atoms to reduce free radicals that are harmful to the human body [4; 5]. Caffeic acid has several benefits for the human body due to its antioxidants and its antibacterial, anti-inflammatory, and immune-modulating compounds [6; 7; 8; 9]. Several methods are used for the analysis of caffeic acid in samples of natural origin: Folin-Ciocalteu [10; 11; 12; 13], high-performance liquid chromatography (HPLC) [14; 15; 16; 17], spectrometric [18; 19; 20] methods, and electrochemical methods [21; 22; 23]. Electrochemical methods, compared to other analytical methods, have a number of advantages, such as simplicity, ability to measure process kinetics, quantification of analysts in real time, low cost, few reagents being required, short analysis time, and high sensitivity, usually with limits of detection in the range from micromolar to nanomolar [24; 25; 26]. However, new biosensors, especially enzyme-based ones, have been developed to increase the sensitivity and especially the selectivity [27; 28; 29; 30]. The use of enzymes in making new biosensors is of great interest, and enzyme-rich plant extracts have been used to obtain biosensors with adequate analytical performance that are useful for the practice. One biological material that can be used to extract an important enzyme, peroxidase, is horseradish root [31; 32]. Peroxidase is an enzyme of the oxidoreductase class, which uses hydrogen peroxide as an electron acceptor. In turn, the enzyme accepts the electron made available by caffeic acid, which behaves as an antioxidant agent [33]. This process underlies the possible detection of caffeic acid and other antioxidant compounds based on biosensors containing peroxidase on the receptive element. Several types of peroxidase-based biosensors have been reported in the literature for the detection of various phenolic compounds. The most important peroxidase-based biosensors used for the detection of some phenolic compounds, the sensitive material, the detection technique, and the substrate (analyte) and detection limits (LOD) are all shown in Table 1.  
In recent years, as can be seen in Table 1, numerous electrochemical biosensors have been developed for the sensitive detection of phenolic compounds with various chemical structures using commercial peroxidase as a biocatalyst. The main advantages of the enzymatic biosensors for detecting different analysts are the easy fabrication, the reproducibility of the fabrication process, and the good stability when compared to the affinity biosensors, which have limited application in the analysis of real samples due to the variability of the antibody production process and the short shelf life of the antibodies. However, the disadvantages include high costs and the loss of the biocatalytic properties of the enzyme during the purification process and storage. Therefore, the development of the novel biosensors, such as those fabricated and characterized in this study, based on enzymes directly extracted from the natural sources and screen-printed technology, could feasibly be used in the screening analysis. The use of raw extract without the purification steps could significantly reduce the costs and open new perspectives regarding the use of natural products in the development of biosensors.