Determination of l-phenylalanine by cucurbit[7]uril sensitized fluorescence quenching method

Determination of L-Phenylalanine in Human Plasma Samples with New Fluorometric Method

The measurement of phenylalanine in biological fluids for the diagnosis of phenylketonuria (PKU) in newborns and the monitoring/therapeutic drug monitoring of individuals with PKU are especially important. Owing to the importance of PKU monitoring in clinical medicine, a new fluorometric method was developed for the determination of L-phenylalanine in serum samples. This method is based on the relationship between phenylalanine ammonia-lyase (PAL) and o-phthalaldehyde (OPA). PAL catalyzes the conversion of phenylalanine to ammonia and trans-cinnamic acid. The formed ammonia reacts with OPA in the presence of sodium sulfite, giving a fluorescent product. The presence of sulfide in an alkaline environment prevents OPA from reacting with other amino acids while allowing it to react only with ammonia. Method characterization and optimization studies, such as the effects of pH, temperature, and interferents, were carried out. The amount of L-phenylalanine in a human serum sample was successfully determined by using the fluorescence emission intensity of the fluorescent product formed as a result of the reaction between OPA and ammonia. The linear range of the method is between 10 μM and 10 mM. The obtained result showed good agreement with the results of the biochemistry analysis laboratory. Recoveries of 95.41% and 73.39% were obtained for phenylalanine and ammonia, respectively. This PAL-OPA-based fluorometric method for phenylalanine is practical, easy to operate, low cost, highly sensitive, and selective and can also be used for the simultaneous determination of ammonia in human serum samples.

A Review on Electrochemical Sensors and Biosensors Used in Phenylalanine Electroanalysis

Phenylalanine is an amino acid found in breast milk and in many foods, being an essential nutrient. This amino acid is very important for the human body because it is transformed into tyrosine and, subsequently, into catecholamine neurotransmitters. However, there are individuals who were born with a genetic disorder called phenylketonuria. The accumulation of phenylalanine and of some metabolites in the body is dangerous and may cause convulsions, brain damage and mental retardation. Determining the concentration of phenylalanine in different biologic fluids is very important because it can provide information about the health status of the individuals envisaged. Since such determinations may be made by using electrochemical sensors and biosensors, numerous researchers have developed such sensors for phenylalanine detection and different sensitive materials were used in order to improve the selectivity, sensitivity and detection limit. The present review aims at presenting the design and performance of some electrochemical bio (sensors) traditionally used for phenylalanine detection as reported in a series of relevant scientific papers published in the last decade.

Reversible Shape-Morphing and Fluorescence-Switching in Supramolecular Nanomaterials Consisting of Amphiphilic Cyanostilbene and Cucurbit[7]uril

We demonstrate a reversible shape-morphing with concurrent fluorescence switching in the nanomaterials which are complexed with cucurbit[7]uril (CB[7]) in water. The cyanostilbene derivative alone forms ribbon-like two-dimensional (2D) nanocrystals with bright yellow excimeric emission in water (λ_em =540 nm, Φ_F =42 %). Upon CB[7] addition, however, the ribbon-like 2D nanocrystals immediately transform to spherical nanoparticles with significant fluorescence quenching and blue-shifting (λ_em =490 nm, Φ_F =1 %) through the supramolecular complexation of the cyanostilbene and CB[7]. Based on this reversible fluorescence switching and shape morphing, we could demonstrate a novel strategy of turn-on fluorescence sensing of spermine and also monitoring of lysine decarboxylase activity.

A supramolecular indicator displacement assay for acetyl amantadine, a proxy biomarker for spermidine/spermine N1-acetyltransferase (SSAT) activity

Acetyl amantadine (AcAm) is produced from amantadine (Am) in vivo upon catalysis by spermidine/spermine N1-acetyl transferase (SSAT). SSAT is a biomarker for multiple aggressive cancers, and the analysis of AcAm in urine has been promoted as a proxy measure for the early detection of cancer. We report here the development and optimization of cucurbit[7]uril–dye pair based indicator displacement assay (IDA) for the detection of AcAm in solution. In deionized water, using Rhodamine B as the dye, the limit of detection of AcAm was 0.087 μM with a linear response range from 0 to 1 μM. Using berberine as the dye, the limit of detection was 0.077 μM with the same range of linear response. Our efforts and difficulties in translating this assay to function in human urine are also described. We achieve a partial response of the berberine IDA to the presence of AcAm in urine that has undergone a simple PD-10 desalting step.