•This review summarises recent advances in electrochemical sensors for forensic drug analysis.•Various strategies for analysing street and biological samples.•Strategies addressing the sample matrix of typical forensic samples.•The challenges and future perspectives for electrochemical forensic drug sensors.Electrochemical-based sensors are a powerful analytical tool which can be exploited by the forensic community particularly for the analysis of illicit substances from street and biological samples. This report presents a brief overview on selected recent publications related to the application of electrochemical sensors to forensic drug analysis and gives opinions on the technical developments as well as the future applications in this field.Download high-res image (139KB)Download full-size image

•A set of only four highly tissue specific tDMR markers is sufficient for reliable and robust body fluid identification.•A multiplex assay was developed for simultaneous detection of these fluids.•The multiplex assay can be applied to single source fluids as well as mixtures.•The components of mock crime scene stains were successfully identified.Potential forensic use of tissue-specific DNA methylation markers has recently been discussed for the identification of the biological source of a stain. In this study 13 promising markers were evaluated to identify suitable candidate markers for the development of a robust and reliable multiplex assay. The results of this study suggest that a combination of only four highly informative markers will be enough for clear body fluid identification. A multiplex assay was developed for the identification of menstrual blood, saliva, semen, and venous blood. This assay was successfully applied to the identification of these body fluids in mixtures and crime scene stains. The multiplex assay aids in the identification of not only single source body fluids but also of body fluid mixtures. The main advantage of using DNA methylation assays over alternative tests is that it can be applied at a later time point in the investigative process since testing is possible even after DNA analysis.

The incorporation of 2,1,3-benzothiadiazole units within the arms of a trigonal quarterfluorene–truxene star-shaped system leads to a monodisperse material with stable multi-electron p- and n-doped states and highly efficient yellow electrogenerated chemiluminescence (ECL). The quantum yield for ECL is 7 times greater than that of the common blue ECL emitter 9,10-diphenylanthracene (DPA).

Direct detection of medically relevant biomarkers in whole blood without the need for pretreatment or extraction is a great challenge for biomedical analysis and diagnosis. Electrochemical techniques, such as electrochemiluminescence (ECL), are promising tools for this area of analysis. ECL offers high sensitivities together with the ability to obtain time and spacial control over the process. This work exploits these features together with the low background signals obtained from ECL detection to clearly identify and quantify dopamine in whole blood with relative standard deviations lower than 5% (n = 5). This near-infrared quantum dot based ECL sensor displayed a linear response over the range 3.7 ≤ [dopamine] ≤ 450 μM, allowing the rapid detection of dopamine and providing a platform for future development. Significantly, the near-infrared quantum dots exhibited excellent penetrability through biological samples such as whole blood, and show the ECL detection of dopamine in whole blood for the first time. This will likely be at the forefront of development in biosensing and imaging fields in the foreseeable future.

This work exploits the high-affinity of recombinant antibodies and low background electrochemiluminescence (ECL) for cardiac-biomarker detection. The developed assay is capable of fg mL−1 detection limits as well as the detection of C-Reactive Protein (CRP) over a clinically relevant range. The assay demonstrated robust reproducibility, selectivity and stability while also highlighting a novel platform for detection of cardiac biomarkers at low concentrations.

The electrochemiluminescent (ECL) properties of a luminescent metal centre, [Ru(bpy)3]2+, can be significantly modulated through its electronic interaction with neighbouring centres and the polymer backbone used to confine it on an electrode surface. From the perspective of ECL based sensing devices, an increase in the ECL efficiency of a metallopolymer film can result in enhanced sensor sensitivity and selectivity. This work probes the ECL properties of both conjugated, [Ru(bpy)2(PPyBBIM)10]2+, and non-conjugated, [Ru(bpy)2(PVP)10]2+, ruthenium based metallopolymer films based on a well documented reaction with sodium oxalate, where bpy is 2,2′-bipyridyl, PPYBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and PVP is poly(4-vinylpyridine). Through a combination of ground state electrochemical studies and ECL measurements, the ECL efficiency for each film is determined. This study reveals that despite a dramatic influence in charge transfer rates between metal centres, as observed for the conducting polymer, mediated through the conducting polymer backbone, a corresponding increase in ECL efficiency is not always observed. The degree of communication between the adjacent excited state metal centres are an important consideration for ECL enhancement however self quenching, luminophore distribution and film porosity must also be considered.

Emission spectroscopy and electrochemistry has been used to probe the electronic communication between adjacent metal centres and the conjugated backbone within a family of imidazole based metallopolymers, [Ru(bpy)2(PPyBBIM)n]2+, in the ground and excited states, bpy is 2,2′-bipyridyl, PPyBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and n = 3, 10 or 20. Electronic communication in the excited state is not efficient and upon optical excitation dual emission is observed, i.e., both the polymer backbone and the metal centres emit. Coupling the ruthenium moiety to the imidazole backbone results in a red shift of approximately 50 nm in the emission spectrum. Luminescent lifetimes of up to 120 ns were also recorded. Cyclic voltammetry was also utilized to illustrate the distance dependence of the electron hopping rates between adjacent metal centres with ground state communication reduced by up to an order of magnitude compared to previously reported results when the metal to backbone ratio was not altered. DCT and De values of up to 3.96 × 10−10 and 5.32 × 10−10 cm2 S−1 were observed with corresponding conductivity values of up to 2.34 × 10−8 S cm−1.

The incorporation of 2,1,3-benzothiadiazole units within the arms of a trigonal quarterfluorene–truxene star-shaped system leads to a monodisperse material with stable multi-electron p- and n-doped states and highly efficient yellow electrogenerated chemiluminescence (ECL). The quantum yield for ECL is 7 times greater than that of the common blue ECL emitter 9,10-diphenylanthracene (DPA).

Emission spectroscopy and electrochemistry has been used to probe the electronic communication between adjacent metal centres and the conjugated backbone within a family of imidazole based metallopolymers, [Ru(bpy)2(PPyBBIM)n]2+, in the ground and excited states, bpy is 2,2′-bipyridyl, PPyBBIM is poly[2-(2-pyridyl)-bibenzimidazole] and n = 3, 10 or 20. Electronic communication in the excited state is not efficient and upon optical excitation dual emission is observed, i.e., both the polymer backbone and the metal centres emit. Coupling the ruthenium moiety to the imidazole backbone results in a red shift of approximately 50 nm in the emission spectrum. Luminescent lifetimes of up to 120 ns were also recorded. Cyclic voltammetry was also utilized to illustrate the distance dependence of the electron hopping rates between adjacent metal centres with ground state communication reduced by up to an order of magnitude compared to previously reported results when the metal to backbone ratio was not altered. DCT and De values of up to 3.96 × 10−10 and 5.32 × 10−10 cm2 S−1 were observed with corresponding conductivity values of up to 2.34 × 10−8 S cm−1.