A photoluminescent nanopaper integrated with molecularly imprinted polymer with a smartphone readout towards selective diagnosis of phenylketonuria

Phenylketonuria (PKU) is an inherited disorder of metabolism that causes an increase in the blood of a chemical known as phenylalanine. Phenylalanine comes from a person s diet and is used by the body to make proteins. Women who have high levels of phenylalanine during pregnancy are at high risk for having babies born with mental retardation, heart problems, small head size (microcephaly) and developmental delay. PKU is usually diagnosed through newborn screening testing that is done shortly after birth on a blood sample (heel stick). Since the phenylketonuria disease is directly related to the amount of L-phenylalanine in blood, it can be controlled by changing the amount of this enzyme. Conventional methods for detection of L-phenylalanine have good performance; however they are not suitable to be utilized as user-friendly methods because the most of them are time-consuming and require sophisticated and expensive instruments and trained operators that limit their applications. Herein, we present a cost-effective, selective, fast and easy-to-use sensing bioplatfrom integrated with molecularly imprinted polymer (MIP) with a smartphone readout for selective determination of L-phenylalanine level in blood. The developed sensing platform consists of two parts: separation and sensing. During the preliminary experiments it was found that the fluorescence (FL) intensity of graphene quantum dots (GQDs) embedded in bacterial cellulose (BC) nanopaper could be dramatically quenched by Cu2+ due to binding the Cu2+ as a FL quencher to the surface of GQDs. But, in the presence of L-phenylalanine, Cu2+ ions prefer to bind to L-phenylalanine and subsequently are released from the surface of GQDs owing to their high affinity toward L-phenylalanine. Hence, upon addition of L-phenylalanine the FL of GQDs/BC-Cu2+ is recovered (“turn-off-on” FL strategy). The recovered FL intensity of GQD/BC-Cu2+, which can be monitored visually using a smartphone or spectroscopically using a spectrofluorimeter, was linearly proportional to the concentration of L-phenylalanine in the range of 10-1000 µg mL-1 and was utilized as an analytical signal for L-phenylalanine sensing. Building upon the fascinating features of BC nanopaper as a very promising bioplatform in optical (bio)sensing applications we are confident our developed sensing bioplatform could be potentially used as a selective, cost-effective, portable, rapid and easy-to-use diagnostic device for accurate detection of L-phenylalanine and PKU diagnosis at the point-of-care and clinical laboratories as well.