Ag-Nanostars for the Sensitive SERS Detection of Dyes in Artistic Cross-Sections—Madonna della Misericordia of the National Gallery of Parma: A Case Study

Abstract

In historical paintings, the detection of low amounts of pigments and dyes by Raman spectroscopy can sometimes be challenging, in particular for fluorescent dyes. This issue can be overcome by using SERS (surface-enhanced Raman spectroscopy) which takes advantage of the properties of nanostructured metal surfaces to quench fluorescence and enhance Raman signals. In this work, silver nanostars (AgNSs) are applied for the first time to real art samples, in particular to painting cross-sections, exploiting their effective SERS properties for pigment identification. The case study is the Madonna della Misericordia of the National Gallery of Parma (Italy). Cross-sections were analyzed at first by optical microscopy, SEM-EDS, and micro-Raman spectroscopy. Unfortunately, in some cross-sections, the application of conventional Raman spectroscopy was hindered by an intense background fluorescence. Therefore, AgNSs were deposited and used as SERS-active agent. The experimentation was successful, allowing us to identify a modern dye, namely copper phthalocyanine. This result, together with the detection of other modern pigments (titanium white) and expert visual examination, allowed to reconstruct the painting history, postdating its realization from the 15th century (according to the Gallery inventory) to 19th century with a heavy role of recent (middle 20th century) restoration interventions.

SERS using nanostar‐in‐cavity structures

“…The tip‐to‐tip maximum span of the AgNS is between 120 and 200 nm, in agreement with previous findings. [ 9,13,14 ] In both cases, it can be observed that the AgNS are deposited partly inside the cavities and partly outside. Comparison between the SEM images in Figure 1, both at low and high magnification, shows that for the 600‐SSV structures each individual cavity typically hosts multiple AgNSs, with the situation of one AgNS in one cavity being a rarer event than for the 220‐SSV structures.…”

Surface Enhanced Raman Spectroscopy With Electrodeposited Copper Ultramicro-Wires With/Without Silver Nanostars Decoration

“…In order to test the Raman enhancement effect produced by these copper-based SERS substrates, benzenethiol (BT) [ 50 , 51 , 52 , 53 , 54 , 55 , 56 , 57 , 58 , 59 ] was chosen as reference Raman probe. A copper plate, named hereafter macro-copper, was employed as control.…”

“…Colloidal dispersions of silver nanostars (AgNSs) were prepared using the one-pot method previously described [ 45 , 50 , 51 ] where hydroxylamine, citrate, and NaOH were used as reducing and shape directioning agents.…”

Futuristic Advancements in Biomass‐Derived Graphene Nanoassemblies: Versatile Biosensors for Point‐of‐Care Devices

“…At a low concentration level presence of fluorescence makes molecular identification difficult. [129,130] The surface-Enhanced Raman spectroscopy (SERS) technique makes use of the Raman signals to detect analyte and this field has gained a lot of interest recently, Figure 9. In 1973 Fleischmann, Hendra, and McQuillan are the first ones to introduce this technique by adding nanostructured metals which decrease fluorescence interference and increase the strength of weak signals [131] and this happens only when the excitation energy of laser and metal substrate surface plasmon energy are close to each other and this technique is named as electromagnetic enhancement.…”