## 1 Introduction
Therefore, some substrates in these paths increase or are switched into different paths. Accordingly, amino acids complications are biochemically outlined by unusual levels of single or several amino acids and their downstream plasma and/or urine metabolites. Amino acid abnormalities are performed with variable and often nonspecific clinical symptoms. In alliance with medical assistance, these disorders are handled by nutritional constraints, supplements, and pharmaceutical food. In this sense, diseases due to amino acid disorders are one of the most dangerous metabolic diseases owed to their deadly repercussions on nurslings. In particular, the most common diseases due to amino acid disorders are phenylketonuria (PKU), tyrosinemia, homocystenuria, arginase deficiency and maple syrup urine smelling disease (MSUD). All the particular strokes enjoy resemblances in clinical expression, generating mental obstruction in neonates, dementia, or are correlated with syndromes such as Parkinson's disease. They can also induce liver failure, rickets, hepatocarcinoma and death without medication in the early stage of essence [15; 16]. Equivalently, a lack of these items can produce hypochondria, depression or albinism [16; 17]. The case of MSUD is a scarce metabolic malady alongside a preponderance of 1:200,000 living childbirth [15]. It is provoked by tremendous amounts of the L-branched-chain amino acid (b AAs), such as leucine, isoleucine, and valine (Leu, Ile, and Val, biomarkers) [18]. In aforementioned malady, these excessive elevations of b AAs provoke complications liver illness, neurological impairments, and indeed death. To prevent these problems, it is particularly notable to obtain a timely and rapid diagnosis in the prime periods of life [14; 15]. The most common methodologies that are used in the determination of branched-chain amino acids and therefore MSUD, are MS/MS, enzyme activity assays, HPLC, capillary electrophoresis, and genetic testing [19; 20; 21; 22; 23; 24; 25; 26; 27]. Notwithstanding, all the practices are time exhausting and, in a few incidents, crave a huge sample volume. A supplementary obstacle relevant to the diagnosis is the matter that for the newborn the monitoring criteria are different among various countries, and indeed vary in the same country, which makes it more troublesome to diagnose MSUD. In addition, there is no end treatment, but dietary constraints are pinpointed and accordingly, repeated monitoring of the target molecule should be performed during the patient's life to evade injurious influences. Problems related to the diagnosis and monitoring of MSUD or the detection of L b AAs underscore the need for developing new diagnostic methods using easier-to-use, low-sample-volume approaches, which is particularly important in neonates [28; 29; 30]. These requirements are met by electrochemical methods and electrochemical (bio)sensors, which are a reliable and profitable appliance for the determination of metabolic biological markers, in order to facilitate their use in the diagnosis and monitoring of this scarce disease, due to their ease of use, simplicity, selectivity, sensibility and low cost [31; 32]. In this manner, electrochemical method could be expanded in early diagnosis of other inborn errors of metabolism, including carbohydrate, fatty acid, and amino and organic acids-based diseases [33]. As it can be seen by the lack of literature, electrochemical sensors have been rarely used in the detection of b AAs related to rare diseases such as MSUD clinical diagnostics. Therefore, in this review, electrochemical (bio)sensors for the determination of branched-chain amino acids are summarized.