**1. Introduction**

Plasmonic nanostructures attract increasing attention as signal amplifiers and transducers for optical sensing. The local plasmon-induced enhancement of electric fields affects various optical processes in molecular systems and therefore finds multiple applications in enhanced spectroscopic techniques, such as Surface-Enhanced Raman Scattering (SERS), Plasmon-Enhanced Fluorescence (PEF), Surface-Enhanced Infrared Absorption (SEIRA), etc. These plasmon-enhanced spectroscopic methods have been described in several recent review articles [1–3].

A wide number of naturally occurring biomolecules, including amino acids, sugars, and nucleotides, are chiral and often exist only in one of the two possible enantiomeric forms [4–6]. It is known that the therapeutic effect of chiral drugs is associated with one of enantiomer's form, while the other one can lead to highly undesirable effects [6]. This fact highlights the necessity of enantiomers detection and separation as well as the need for stereoselective synthesis. Circular dichroism (CD) spectroscopy is usually used for analyzing molecular chirality. It determines small differences in the interactions between left- and right-circularly polarized light (CPL) with a molecular system. Molecular chirality can also reveal itself by rotating a polarization plane of linearly polarized light, an effect called optical rotational dispersion (ORD). These chiroptical responses define each other through Kramers-Kronig relations [7]. Unfortunately, their experimental detection is possible only in highly concentrated analytes because the chiroptical signals are usually very weak. Thus, there is great interest in chiral plasmonics nowadays, especially in using plasmon-enhanced near fields in order to increase the sensitivity of chiroptical

spectroscopy [8, 9]. Many chiral plasmonic nanostructures are studied both experimentally and theoretically. The nature of plasmonic chirality and the chiroptical effects in plasmonic nanostructures are described in several extensive reviews [10–12].

This chapter is dedicated to the applications of different plasmonic metal nanostructures and their hybrid nanosystems with optically active organic and biomolecules in chiral biosensing. We focus on the recently published results of using plasmon-induced evanescent fields and consider the main types of molecular plasmonic systems capable of generating amplified chiroptic signal in order to detect the presence of certain biomolecules and (in some cases) to determine their orientation and high-order structure.
