Heavy metals ions (HMI), if not properly handled, used and disposed, are a hazard for the ecosystem and pose serious risks for human health. They are counted among the most common environmental pollutants, mainly originating from anthropogenic sources, such as agricultural, industrial and/or domestic effluents, atmospheric emissions, etc. To face this issue, it is necessary not only to determine the origin, distribution and the concentration of HMI but also to rapidly (possibly in real-time) monitor their concentration levels in situ. Therefore, portable, low-cost and high performing analytical tools are urgently needed. Even though in the last decades many analytical tools and methodologies have been designed to this aim, there are still several open challenges. Compared with the traditional analytical techniques, such as atomic absorption/emission spectroscopy, inductively coupled plasma mass spectrometry and/or high-performance liquid chromatography coupled with electrochemical or UV–VIS detectors, bio- and biomimetic electrochemical sensors provide high sensitivity, selectivity and rapid responses within portable and user-friendly devices. In this review, the advances in HMI sensing in the last five years (2016–2020) are addressed. Key examples of bio and biomimetic electrochemical, impedimetric and electrochemiluminescence-based sensors for Hg²⁺, Cu²⁺, Pb²⁺, Cd²⁺, Cr⁶⁺, Zn²⁺ and Tl⁺ are described and discussed.

Terahertz time-domain (THz-TD) imaging plays an increasingly significant role in the study of solid-state materials by enabling the simultaneous extraction of spectroscopic composition and surface topography in the far-infrared region (3–300 cm⁻¹). However, when applied to works of art in reflection configuration, significant challenges arise, including weak signal intensity, multiple signal losses, and surface distortion. This study proposes a practical solution to overcome these limitations and conducts an integrated imaging and spectroscopic analysis on painted fresco surfaces, allowing for the retrieval of surface thicknesses, material distribution, and pigment spectroscopic signals. The study addresses the issue of surface geometrical distortion, which hampers the accurate determination of the THz phase signal. By tackling this challenge, this work successfully determines the absorption coefficient for each point on the surface and retrieves spectroscopic signatures. Additionally, the temporal deconvolution technique is employed to separate different layers of the sample and differentiate between outer and inner surface topography. The objective of this study is to demonstrate the advantages and limitations of THz-TD imaging in determining surface thicknesses, material distribution, and pigment spectroscopic signals. The results obtained highlight the potential of THz-TD imaging in investigating painted works of art, offering new possibilities for routine analysis in the field of cultural heritage preservation.