br Materials and methods br Results
Materials and methods
Results and discussion
Declaration of interest statement
Acknowledgment This work was supported by the National Natural Science Foundation of China (No. 21775132, 21505112), Scientific Research Foundation of Hunan Provincial Education Department (No. 16A204), Hunan 2011 Collaborative Innovation Center of Chemical Engineering & Technology with Environmental Benignity and Effective Resource Utilization, the project of innovation team of the Ministry of Education (IRT_17R90) and “1515” academic leader team program of Hunan Agricultural University.
Introduction Simple as its structure is, histidine, one of the 20 amino acids, functions as an indispensable LB Broth, Miller in series of important protein assembling inside our body. As previously reported, this semi-essential bioactive molecule contributes to some particularly key biological system including cell and tissue repair after accidental trauma [1,2], metallic–enzymatic reactions  and the intracellular homeostasis of some metal ions like copper. However, what makes His favored by physician-scientists is its function as a neurotransmitter or some other unknown part in the mysterious nervous system [, , ]. The typical level of l-histidine in body is 0.31–26.35 mg/mL by and large. Insufficiency of l-histidine leads to certain illnesses, while the profusion of l-histidine with more than 29.5 mg/mL results in histidinemia . Besides, counting on the functions above, the pathophysiological processes of many sets of diseases, such as chronic kidney disease , Alzheimer's disease , pulmonary disease  and cancer  was reported to be associated with Histidine. Considering the importance of l-histidine, it would be attracting to develop a facile and low-cost sensing strategy for it. Traditional analytical methods such as capillary electrophoresis [, , , , , ], mass spectrometry  and high-performance liquid chromatography [, , , , , ] have been the most common methods for l-histidine detection. However, these methods are usually low sensitive, complicated, dearly expensive, and time-consuming because of the involvement of the complex sample pretreatment procedures. In order to overcome these limitations, some ancient methods were improved, and many rapid and simple analytical strategies based on fluorescent [, , , , , , , , , , ], electrochemical voltammetry [, , ], nuclear magnetic resonance , spectroscopy  and colorimetric [, , , , ] have been established. Zhou et al. built up a classical portable chemical sensor using a combination of the personal glucose meters (PGM) with click chemistry for l-histidine detection with a great limit of 3.4 nM among many other chemical sensors . Zhang's group explored a novel fluorescent sensor of Histidine and Cysteine by utilizing AMP-Tb as a fluorescent probe with enhanced fluorescence power corresponding to the concentration of Histidine and Cysteine respectively in the range from 0.2 to 150 μM and 0.5 to 200 μM, which not only shows its short range, but also its poor selectivity . Liu's team synthesized histidine-Au nanoclusters providing a highly selective detection of histidine. In real sample detection they endeavor to apply to human blood plasma, however, it seems unpractical and not cost-effective in medical use with their constrained detection limit range . Mobarraz et al. have synthesized l-cysteine capped-ZnS quantum dots, and they reported that histidine could effectively quench the quantum dots emission more than other amino acids which showed 4 times decreased than other amino acids . However, in our test, the difference will be more obvious both in visual and in the database with more than 8 times. Most of the detection methods for l-histidine are costly, complicated and unwieldy optical detection scheme. As we all know, in optical detection strategy, the volume of the specimen assumes to be an essential part of sensitivity since the absence of the volume influences the coveted sensitivity. The constraint in detection limit is a noteworthy consideration of the optical detection strategy for the analysis of amino acids. Moreover, complication of labeling process and inconveniences of dealing with instrument are the real bottleneck of the optical strategy for detection. These shortcomings mentioned above in optical plan can be expelled by colorimetric method which is extinct with excellent convenience due to the unique advantage of not requiring confused instrumentations, and the detection of l-histidine with naked eye expected to be more suitable and practical in medical applications.