Karlo Maškarić

Aggregation of silver nanoparticles (AgNPs) induced by halide ions has been widely exploited within the surface-enhanced Raman scattering (SERS) applications, acting as adions for improved detection of specific analytes. Both cations and anions exert influence on SERS and studies so far have focused on salt concentrations ranging within millimole range to induce optimal AgNPs aggregation. Here we employed hypersaline solutions (1-2 M, with 0.2 M increments), simulating the salinity levels of hypersaline environmental waters, without considering additional contributors, and demonstrated that SERS can be reliably used to estimate the salinity of such samples. We employed the strong interaction between excessive chloride ions and citrate-reduced AgNPs surface to investigate the SERS signal variability, focusing on the Ag/Ag-Cl SERS band at 231 cm⁻¹ over time, starting from the moment the saline solution was mixed with AgNPs until a stable plateau of maximum intensity was reached (240 minutes). The complex physicochemical mechanisms of AgNPs aggregation enabled the time-dependent intensity plot of the 231 cm-1 band as a function of saline solution concentration. A calibration curve against concentration based on exponential function fitting of the SERS dataset allowed to calculate the concentration of unknown hypersaline solutions. The calibration curve corresponding to ten minutes after mixing solutions proved to be the most accurate, with an R² value of 0.99, with relative error < 1.5% for NaCl concentration estimates. These results expand the SERS applicability for fast, in situ salinity estimation in hypersaline aquatic environment.

An unusual blue-purple shell coloration was observed in specimens of Rapana venosa collected as discarded biogenic carbonate along the Romanian Black Sea coast. This chromatic feature has not previously been reported for this species, which is typically characterized by a grey-brown exterior and bright orange-pink aperture. Despite the ecological and economic relevance of this veined rapa whelk, the chemical nature of its shell pigments remains poorly understood. Here, we present a comprehensive molecular and structural characterization of the pigments responsible for this atypical coloration.,Resonance and non-resonance Raman microspectroscopy with multiple excitation wavelengths were employed, complemented by surface-enhanced Raman scattering (SERS), Fourier-transform infrared spectroscopy (FT-IR), powdered X-ray diffraction (XRD), and SEM-EDX analysis. Raman analyses revealed the coexistence of aragonite and calcite with a clear cross-sectional gradient, aragonite being enriched in the inner shell layers and calcite towards the exterior. Pigment distribution was strongly excitation-wavelength dependent. Spectroscopic data excluded indigotin derivatives and caroteno-protein complexes as major chromophores responsible for the blue colouration. Instead, the coloration arises from a complex mixture of endogenous methylated polyenes with different conjugation lengths, including species with partial triple-bond character, embedded within the mineral-organic matrix. These polyenes coexist and interact with melanins and porphyrin-type compounds, producing the observed blue-purple hue. SERS analysis of ethanol extracts identified β-carotene at sub-micromolar levels as the only solvent-extractable carotenoid, confirming that the dominant polyenes are non-extractable and structurally bound within the shell framework.,This study reveals a previously unrecognized polyene-based pigment system in Rapana venosa shells and demonstrates how pigment-biomineral interactions and molecular conjugation length contribute to shell coloration, providing new insights into the naturally occurring polyenic chromophores in biomineralized tissues.

The brine shrimp Artemia salina (Linnaeus, 1758) has been used for ecotoxicity testing, both in field and laboratory settings. Carotenoid composition of A. salina plays a role in mitigation of physiological stress and maintaining homeostasis. We exploited the fact that carotenoids are easily detectable under resonance Raman (RR) conditions by conducting in-vivo Raman measurements on A. salina. Here we report for the first time the in vivo characterization of A. salina pigments using RR spectroscopy and, based on these results we further explored the carotenoid profile of this crustacean as a proxy to readout the environmental parameters variability of hypersaline lakes from a balneary resort during cold and warm season. The in vivo carotenoids characterization is feasible using RR spectroscopy, Lorentz deconvolution of the main carotenoid ν1(C=C) band revealed up to five peaks; implying spatio-temporal variations in carotenoid species content. Spectral features of peak positions and area of these deconvoluted bands revealed variations between cold and warm season. Contribution of specific carotenoid species can be connected to parameters such as salinity and nutritional resource availability which affect conversion of carotenoids by A. salina. These findings demonstrate in-vivo Raman measurements of A. salina could provide relevant and valuable informations for ecological, ecotoxicological, and biological studies of A.salina.

Seafood-derived carbonate waste, primarily calcium carbonate (CaCO₃), has attracted growing interest for sustainable reuse, yet the unique potential of aged biogenic sources remains underexplored. Blue crab (Callinectes sapidus) shells are particularly distinctive: they consist of Mg-calcite with an intrinsic 3D-porous structure and naturally embedded astaxanthin, a potent antioxidant not found in other calcite- or aragonite-based residues. While organic degradation over time is often assumed to compromise functionality, this study demonstrates that five-years-aged crustacean shell waste retains both its crystallinity and bioactive carotenoids after calibrated ball milling. Across four powder batches produced under distinct milling conditions by varying frequencies and durations, dynamic light scattering confirmed only subtle particle size variation, while Raman spectroscopy, XRD, FT-IR, and SEM-EDX confirmed structural and chemical integrity and highlighted the subtle amorphization induced by slightly different milling parameters, which, in turn, driven to slightly different conversion efficiency into phosphate mineral. Strikingly, all powders underwent rapid transformation into dicalcium phosphate dihydrate (brushite) enriched with carotenoids upon reaction with phosphoric acid. This work reveals, for the first time, that years-aged biogenic Mg-calcite waste not only preserves its naturally embedded carotenoids but also offers a direct route to functional phosphate composites, establishing its untapped value in environmental and biomedical applications.