Molecularly imprinted polymers (MIPs), imprinted for uracil and 5-fluorouracil, were used in the development of electrochemical sensors for selective and sensitive analysis Of uracil and 5-fluorouracil in aqueous and blood plasma samples. The same MIP motif prepared from melamine and chloranil precursors was used for both analytes as a coating material for modification of a hanging mercury drop electrode (HMDE) by a drop-coating method using dimethylformamide casting Solution. This revealed the imprinting versatility of the imprinted polymer, where binding events for both analytes in aqueous environments were transduced into their respective differential pulse, cathodic stripping voltammetric signals with high sensitivity and without any false positive results owing to nonspecific sorptions, interferences and cross-reactivities. The limits of detection (3 sigma) for uracil and 5-fluorouracil were found to be as low as 0.34 and 0.26 ng mL(-1), respectively, which enable substantial sensitivity in the diagnosis of uracil-disorders and fluoropyrimidine toxicity in patients.

Main inborn errors of metabolism diagnosable through uracil (Ura) analysis and the therapeutic monitoring of toxic 5-fluorouracil (5FU) in dihydro pyrimidine dehydrogenase (DPD) deficient patients require a sensitive, reproducible, selective and accurate method. In this work, an artificial receptor in the format of molecularly imprinted polymer (MIP) brush 'grafted to' the surface of sol-gel immobilized on cost-effective homemade solid-phase microextraction (SPME) fibers, individually imprinted with either of Ura and 5FU, was used in combination with a voltammetric sensor duly modified with the same MIP. This combination provided up to 10- and 8.4-fold preconcentrations of Ura and 5FU, respectively, which was more than sufficient for achieving stringent detection limits in the primitive diagnosis of uracil disorders and fluoropyrimidine toxicity in DPD-deficient patients. The proposed method permits the assessment of Ura and 5FU plasma concentrations with detection limits pf 0.0245 and 0.0484 ng mL(-1) (RSD = 1.0-2.5%, S/N = 3), respectively, without any problems of non-specific false-positives and cross-reactivities in complicated matrices of biological samples.

A combination approach in solid-phase microextraction, based on a molecularly imprinted polymer-brush coating on an optical fiber coupled with a complementary molecularly imprinted polymer sensor, has been adopted for isolation, preconcentration, and analysis of dopamine at ultratrace levels in highly dilute aqueous samples. This combination enabled enhanced (up to 8.5-fold) preconcentration of the analyte, which is appropriate for achieving a stringent detection limit in clinical diagnosis of several neurodegenerative diseases. The detection limit of dopamine in biological samples was 0.018 ng mL−1 with a relative standard deviation less than 2.1% and without any non-specific contributions.

The proposed L-histidine sensing system composed of a molecularly imprinted solid-phase microextraction component combined with a molecularly imprinted polymer sensor was used to determine critical levels of test analyte in a complex matrix of highly diluted human blood serum without any non-specific sorption and false-positive contributions. The molecularly imprinted polymer was a zwitterionic polymer brush derived from the disodium salt of EDTA and chloranil, grafted to solid-phase microextraction material. The hyphenated approach was able to detect L-histidine quantitatively with a limit of detection as low as 0.0435 ng/mL (RSD = 0.2%, S/N = 3).

Induced-fit responsive dopamine (DA) imprinted polymer, poly (melamine-co-chloranil), was used as a suitable coating material for the modification of a hanging mercury drop electrode. The zwitterionic conformation of the imprinted polymer responded differential pulse, cathodic stripping voltammetric current, without any false-positive or false-negative contributions of non-specific sorptions, in aqueous environment of complex matrices. The limit of detection (3σ) of dopamine was found to be as low as 0.148ngmL−1, by the proposed sensor that could be considered a sensitive marker of dopamine depletion in Parkinson's disease (PD).

Clinical manifestations owing to ascorbic acid deficiency demand an easy-to-use, rapid, robust and inexpensive technique, which can measure serum ascorbic acid at ultratrace level to attend the problem of hypovitaminosis C and acute cases of scurvy. In the present work, a novel molecularly imprinted polymer (MIP)-coated solid-phase microextraction (SPME) fiber that could be coupled to a complementary MIP-sensor was prepared with ascorbic acid as a template molecule. The characteristics and applications of this fiber were investigated. The same MIP receptor for both SPME and the corresponding sensor was able to enhance the preconcentration of analyte substantially so as to attain the stringent level of sensitivity in highly diluted aqueous, blood serum and pharmaceutical samples. The extraction yield of ascorbic acid (AA) with the MIP-coated fiber was found to be quantitative (detection limit 0.0396ngmL−1, RSD=2.3%, S/N=3) in aqueous samples without any problem of non-specific false positive results and cross-reactivity.