## 5 Sensing Methods for Formaldehyde
### Scopus Data-Base and Analytical Parameter Definition
The sample to be analyzed does not undergo any strong physical-chemical treatment, basically, it is analyzed as it is, which is a strength of such measures. The authors determined different analytical parameters (limit of detection, LOD, 5.0 mg kg\({}^{-1}\), recoveries between 88.6 and 110.6%, and RSD \(<\) 2.76%) but they spent time emphasizing the advantages of this method in relation to the conventional methods in terms of detection time (less than 1 min) and sample volume to be used for the analysis (1-2 \(\mu\)L): these allowed the authors to reduce analysis costs. On the other hand, three recent papers deal with the FA determination in chicken samples [48; 49; 50]. In the first paper, [PERSON] et al. developed a FA sensor from silver nanoclusters (AgNCs) templated by polymethacrylic acid (PMMA) [48]. The authors prepared the [PERSON] reagent ([Ag(NH\({}_{3}\))\({}_{2}\)]\({}^{+}\)) from aqueous ammonia and a basic solution of Ag\({}^{+}\): they used it for differentiating aldehyde from ketone functional groups due to the aldehydes properties to be easily oxidized to carboxylic acids. Simultaneously, they exploited the performance of AgNPsNCs for increasing the detectability of [PERSON] reagent: the authors obtained the AgNPsNCs@Tollens which reacts with FA for giving silver nanoparticles (AgNPs) increasing their size and changing the color according to the FA content. Finally, a FA chemodosimeter allows the determination at 430 nm. The authors investigated the effect both of the pH solutions (maximum absorbance at pH 4.5, it decreased to other pH values), the incubation time (mix time of AgNPsNCs@Tollens and FA was set up at 25 min), the AgNPsNCs concentration and of Ag\({}^{+}\) concentration (0.23 mM and 0.68 mM, respectively, for the best efficiency): according to these parameters, the authors obtained a good linear response (coefficient of determination, r\({}^{2}\), 0.9841) and LOD (27.99 \(\mu\)M), and very high recoveries in chicken (and squid) matrix (100.6-101.7%, standard deviation (sd) \(<\) 2.3), more accurate and precise than those determined by HPLC method (99.5-110.2%, sd \(<\) 6.8). Further, the second paper, [PERSON] et al., deals with the Tollens' reagent: the authors made a complex with gold nanoprism and they formed a gold nanoprism/Tollens' reagent (Au-np/TR) complex as the sensor used in headspace single-drop microextraction (HSSDME) [49]. Basically, FA is extracted by this microextraction using Au-np/TR as a solvent droplet for reaching high enrichment. The authors focused their attention on the characterization of the complex applying techniques such as transmission electron microscopy (TEM) and energy-dispersive X-ray spectroscopy (EDX): they calculated a gold nanoparticle size of 106.5 nm as well as the presence of Ag atoms at 73.4% on the surface of the Au-np. They \begin{table}
\begin{tabular}{c c c c c c c} \hline
**Matrix** & **Analytical Method** & **LOD 1** & **LQ 2** & **LDR 3** & **Recovery (\%)** & **RSD (\%) 4** & **Refs.** \\ \hline \multirow{3}{*}{
\begin{tabular}{c} cow tripe \\ poultry, beef, \\ cooked, muton \\ beef \\ \end{tabular} } & _no sensing determination_ & & & & & & \\ PAD [11] & 100 mg L\({}^{-1}\) & N/A & 100–1000 mg L\({}^{-1}\) & N/A & N/A & [51] \\  & spectrophotometric technique & N/A & N/A & 0–10 ppm & N/A & N/A & [52] \\  & SPME-GC-MS [12] & 25.08 ng g\({}^{-1}\) & N/A & 100–5000 ng g\({}^{-1}\) & N/A & N/A & [53] \\ \hline \end{tabular}  
* \({}^{1}\) LOD: limit of detection; 2 LOQ: limit of quantification; 3 LDR: linear dynamic range; 4 RSD: relative standard deviation; 5 PDMS: polydimethylsiloxane; 6 N/A: not available in the paper; 7 AgNCs: silver nanoclusters; 8 PMMA: polymethacrylic acid; 9 Au-np/TR: gold nanoprism/Tollens’ reagent; 10 MOFs: metal-organic framework; 11 PAD: paper-based analytical device; 12 SPME-GC-MS: solid space microextraction-gas chromatography-mass spectrometry.  
\end{table}