## 5 Sensing Methods for Formaldehyde
### Fish
FTIR and scanning electron microscopy (SEM) were used for characterizing the surface morphology. A screen-printed electrode (SPE) for determining NADH and FA as well, was very recently designed by [PERSON] et al. [57]. They designed a FA dehydrogenase decorated Cys-AuPd-ErGO nanocomposite with fern-like AuPd dendrites deposited on reduced graphene oxide (ErGO) on SPE. The sensor showed direct electron transfer avoiding the use of electron mediators. After sensor characterization by means of SEM, Energy-dispersive X-ray Spectroscopy (EDAX), Raman, and FT-IR spectroscopy, the authors studied the optimal conditions both for analyzing NADH and FA and for minimizing the interferences. In terms of analytical parameters, they reached a very good performance (r\({}^{2}\) 0.991 in the linear range of 1-100 \(\upmu\)M; LOD 0.3 \(\upmu\)M; sensitivity 73 \(\upmu\)A \(\upmu\)M\({}^{-1}\) cm\({}^{-2}\)). According to the interferences,  
\begin{table} \begin{tabular}{c c c c c c c c} \hline
**Matrix** & **Analytical Method** & **LOD** & **LOQ** & **LDR** & **Recovery (\%)** & **RSD (\%)** & **Refs.** \\ \hline \multicolumn{6}{c}{_sensor deterministic_} \\ squid & AgNCs implanted by PMMA & 27,99 \(\upmu\)M & N/A & 30–50 \(\upmu\)M & 100,6-101.7 & \(<\)3 & [48] \\ squid & electronic noise & N/A & N/A & ND & N/A & 0.028-0.143 & [54] \\ squid & PdNPs-PAA/GO/GCE-H-Amp 1 & 16 mmol L\({}^{-1}\) & 53 mmol L\({}^{-1}\) & 50–5000 mmol L\({}^{-1}\) & 94–104.2 & \(<\)3.5 & [55] \\ squid & PEDOT:PSS/MWCNTs-N\({}_{2}\) sensor 2 & 1–10 ppm & N/A & 10–20 ppm & N/A & N/A & [56] \\ fish & Cys-AuPd-ErGO on SPE 3 & 0.3 \(\upmu\)M & N/A & 1–100 \(\upmu\)M & 88–104 & 2.4–4.6 & [57] \\ Seafood 4 & biodegradable hybrid fiber film & 5 ppm & 16.8 ppm & 0–100 ppm & 98.80–104.65 & 0.12–1.21 & [58] \\ seafood & electrochemical biosensors & 0.1 ppm & N/A & 0.01–10 ppm & 81.2–22.2 & 0.32–6.64 & [59] \\ occupus & Au-NP/TR as plasmonic sensor & 30 \(\upmu\)M & \(<\)50 \(\upmu\)M & 0.1–100 \(\upmu\)M & 94–98 & \(<\)5 & [49] \\ snapper & fiber bundle-based sensor & N/A & N/A & 3–21\% & N/A & N/A & [60] \\ spamper fish, & & & & & & & \\ pomfet fish & & & & & & & \\ threadfin fish & & & & & & & \\ _no sensing determination_ & & & & & & \\ squid & paper-based titration & 100 mg mL & N/A & 100–1000 mg L\({}^{-1}\) & N/A & N/A & [51] \\ fish, squid, & & & & & & & \\ shrimp, octopus & & & & & & & \\ fish & PDMS microfluidic chip & 5.0 mg kg\({}^{-1}\) & N/A & 5–400 mg kg & 88.6–110.6 & \(<\)2.76 & [47] \\ fish & HPLC-CAD® & 1.75 mg L\({}^{-1}\) & 5.83 mg L\({}^{-1}\) & 5–100 mg L\({}^{-1}\) & 91.2–105.3 & 6.72 & [63] \\ aquatic products & MoO\({}_{3}\)/PPV intercalative sampling & & & & & & & \\ adsorbent-GC-MS & 0.004 \(\upmu\)g L\({}^{-1}\) & N/A & 0.02–20.35 \(\upmu\)g L\({}^{-1}\) & 75.0–108 & 2.2–6.1 & [64] \\ \hline \end{tabular}   
* PdNPs-PAA-GO/GCE-FI-Amp: poly(acrylic acid)-functionalized graphene oxide modified on a glassy carbon electrode with incorporated flow-injection amperometry; \({}^{2}\) PEDOT:PSS/MWCNTs-N\({}_{2}\) sensor: sensors based on 2D hybrid pristine, NH\({}_{2}\) and N\({}_{2}\) functionalized multi-wall carbon nanotubes conductive polymer; \({}^{3}\)SPE: screen printed electrode; 4 seafood: _Luitrans embariprostitrés, _Eathymthey studied the selectivity related to possible agents such as acetaldehyde, uric acid, KCl, NaCl, ammonia, urea, and nitrate: different experiments were carried out and the related results showed very low interference for KCl, NaCl, ammonia, urea, and nitrate (<4.9) and acceptable one for acetaldehyde (<8.1%). Finally, the sensor was stable over two days and its activity decreased from 42% to 17% after 6-7 days which confirmed the reliability of such a developed device. More interesting from an analytical point of view were the analytical methods developed by [PERSON] et al. [58]: they prepared a biodegradable hybrid polymer film where Nash colorimetric reagents were entrapped. This system was able to change color in presence of FA and the angle formed gave the FA content in the investigated matrix.