# Molecularly-Imprinted SERS: A Potential Method for Bioanalysis
## 1 Introduction  
Bioanalysis is related to drug development, forensic analysis, doping control, and identification of biomarkers for diagnostic methods of various diseases. Bioanalysis also provides information regarding the toxicokinetics, pharmacokinetics and pharmacodynamics of new drugs. Bioanalysis is the analysis of analytes, i.e., drugs, metabolites, and biomarkers, in biological samples (blood, plasma, serum, saliva, urine, feces, skin, hair, and organ tissues). Bioanalysis consists of several stages which include sample collection from preclinical and clinical trials, sample preparation, and bioanalysis stages using certain methods and instruments. The sample preparation stage is the most important stage in a bioanalysis. The role of the sample preparation stage is to remove the influence of the sample matrix, as well as to improve the analytical performance of a bioanalytical method [1]. Sample preparation helps increase the selectivity and sensitivity of bioanalytical methods. Due to the matrix complexity of biological sample, a sample preparation step is required [2, 3]. Liquid-liquid extraction (LLE) and solid-phase extraction (SPE) are two commonly used techniques [1]. Liquid-liquid extraction has limitations, including minimal enrichment factor, inadequate recoveries, and requires large amounts of organic solvents [4]. Solid-phase extraction is usually used for cleaning and pre-concentration in analyzing biological samples due to the simplicity, rapidness, and minimizing of those limitations of LLE [4, 5]. The main drawback of SPE is the selectivity of the sorbent that separates the analytic [5]. The use of SPE in sample preparation, is strongly influenced by selecting the suitable SPE sorbent. A good separation needed a selective and specific sorbent [6]. The SPE sorbent is the determining factor in the ultimate performance of the sample preparation procedure [7]. The most common adsorbent (C\({}_{8}\), C\({}_{18}\), Al\({}_{2}\)O\({}_{3}\), silica)are usually interfered by the sample impurities [8; 9; 10]. Molecularly imprinting technology allows us to create materials that can identify specific molecules to be analyzed and offer high selectivity of bioanalytical method [4]. Molecularly imprinted polymer (MIP) is a materials that mimic antigen-antibody reactions, so it can gained the specific recognition of analytes in sample preparation [11; 12]. Because of that, MIP is widely employed in solid-phase extraction as a sorbent [3; 4; 10; 13; 14; 15; 16; 17; 18; 19; 20; 21; 22; 23; 24]. The use of MIP as a sorbent in SPE, can improve the selectivity, sensitivity and accuracy of the bioanalytical method. Sample preparation is usually followed by detection using analytical instruments, such as HPLC, LC/MS, LC/MS/MS, SERS, electrochemical method, etc. Surface-enhanced Raman spectroscopy is a non-destructive, fast and sensitive method, particularly for trace analysis. The use of SERS depends on enhancement of Raman signal. Signal enhancement in SERS application, can happen if the analytes are adsorbed on rugged metal surfaces (e.g., Au, Ag, and Cu NPs) [25]. SERS has been utilized to detect trace organic chemicals, because of its facile procedure. The matrix interference effect, which includes non-targeted analytes and rugged Raman-like peaks from other molecules such as proteins, lipids, and pigments, prohibits it from being widely employed in complex matrix. The interference effect diminishes analyte sensitivity and can result in Au or Ag nanoparticle colloid precipitates. The matrix complexity of bioanalytical and trace analysis sample, can cause the failure in the enhancement Raman signals of SERS applications. These factors cause an increase in weak signal, matrix effect, and fluorescence interference from the background. These limitations can be overcome by the use of appropriate preparation techniques [26]. The combination of MIP and SERS as a sample preparation and detection method is one of the solution for bioanalysis.