Molecular absorbance and fluorescence measurements are usually performed by benchtop or portable USB spectrophotometers or fluorometers. However, even the simplest configuration of these instruments requires considerable financial input, which is not affordable to many universities and research groups especially when public politics withdraw funds from science. Light-emitting diodes (LEDs) based devices can be an interesting alternative for low-cost, portable yet reliable measurements of absorbance of fluorescence. Especially if associated with the fabrication of 3D structures by additive manufacturing techniques. Although there are many reviews in the literature dedicated to discussing the theoretical aspects and analytical performance of LED-based devices, we consider that these reviews are not easily applicable for beginners in electronics. It results in the intimidation to employ such powerful tools which could have a huge impact mainly to small and/or initial groups. In this tutorial, we present a guide that will help students and researchers to construct “lab-built” devices based on simple optoelectronic components and 3D printing to perform molecular absorbance and fluorescence measurements for analytical methods. Finally, with this tutorial guide, we anticipate a large spread of the usage of LED devices for reliable analytical measurements that can be extensively used in many scenarios.

Formaldehyde is a carcinogenic compound that was employed as fungicide in the past. Despite its disuse, some foods such as mushrooms naturally produce formaldehyde, showing the importance of its determination. In this work, a mechanized flow system based on solenoid valves is proposed for spectrophotometric formaldehyde determination in mushrooms. The analyte was extracted from fresh and dried mushrooms samples by steam distillation with deionized water in the presence of phosphoric acid. The determination was based on the reaction between formaldehyde and acetylacetone in presence of ammonium acetate (Hantzsch reaction), leading to the formation of 3,5-diacetyl-1,4-dihydrolutidine (DDL, λmax = 412 nm). Linear response from 0.2 to 7.0 mg L-1 was achieved, with detection limit estimated at 0.02 mg L-1 (99.7% confidence level). Coefficient of variation and sample throughput were 1.1% (n = 15) and 17 h-1, respectively. Per determination, 11 mg of acetylacetone and 30 mg of ammonium acetate were consumed, generating 4.2 mL of waste. The procedure was applied to formaldehyde determination in fresh and dried shiitake, and fresh shimeji, and the results agreed with those attained by reference method at the 95% confidence level.