Cruciferous Waste Material from Valuable Resource for Nanoparticle-Based Sensors ^†

1. Introduction

Cruciferous vegetables are part of the Brassicaceae family. Vegetables such as broccoli, cauliflower, Chinese cabbage, radishes, arugula, cabbage, Brussels sprouts or horseradish, can be considered functional foods because they maintain healthy bodily functions and prevent chronic inflammation, diabetes, cardiovascular disease, and cancer [1]. The phytochemical profile of these vegetables can vary even within the same plant species, depending on the plant organ studied. For example, cruciferous buds can contain from 2 to 10 times more phenolic compounds compared to roots and inflorescences, the plant components that are otherwise most commonly consumed [2]. The aim of the current study is to obtain extracts rich in phytoconstituents from leaves and seeds of Brassica oleracea var. Italica (Broccoli), Eruca sativa L. (Arugula), Brassica napus oleifera (Rapeseed) and Raphanus sativus L. var. Sativus (Radishes) to phytosynthesize gold nanoparticles (AuNPs) which will be used for further development of sensors.

2. Materials and Methods

In order to extract the phytochemicals from the leaves and seeds of cruciferous vegetables, a classical (at temperature) and a modern method with a microwave digestion system (MILESTONE ETHOS EASY) have been applied, using a solid/liquid ratio of 1:10 (w/v) in both cases, using hydroalcoholic mixture (1:1 v/v water: ethyl alcohol) as the extraction solvent. Furthermore, for the phytosynthesis of mono-metallic NPs each hydroalcoholic extract has been mixed with HAuCl4 solution in a 1:1 ratio v/v. UV-VIS spectrometry was used to assess the formation of gold nanoparticles in the wavelength range of 400–650 nm.

3. Results

The formation of NPs was monitored by UV-VIS spectrometry, in the wavelength range of 400–650 nm. The UV-Vis spectra present the characteristic absorption peak for gold nanoparticles between 500–550 nm (Figure 1), better defined in case of phytosynthesised NP with Mw extract.

4. Conclusions

The results suggest that AuNPs were synthesized in both cases using the extracts obtained by the two extraction methods. It can be concluded that the microwave extraction method, compared to the classical one, significantly improves the recovery of phenolic compounds from cruciferous vegetables.