Cocaine sensor

There is considerable interest in the design of biosensors for drugs of abuse (cocaine, heroin, morphine, etc.), as well as for prescription pharmaceutical compounds (see 267,325, and 326 for reviews). Typically these sensors are of the liquid membrane type, containing an organic compound reactive to the drug. A cocaine sensor, for example, consists of a PVC membrane plasticized with dibutyl phtalate, and containing tetraphenylborate as the active substance. A strychnine sensor uses a liquid membrane electrode based on ion pairs of strychnine with picrolonate or tetrakis (3-methylpheny)borate. 

A polyvinyl chloride membrane electrode for heroin based on an ion-pair complex with tetraphenylborate is described (328). The sensor shows a near-Nernstian response over the heroin concentration range 0.01 M to 0.1 mM, with good selectivity for heroin in the presence of a number of adultercuits and base compounds present in illicit heroin powders. A cocaine sensor proposed by Zeng (329) uses a cocaine picrylaminate membrane. The calibration curve is linear in the range 0.01 M to 10 iM, with a coefficient of variation of less than... 

J. Halamek, A. Makower, K. Knosche, P. Skladal and F.W. Scheller, Piezoelectric affinity sensors for cocaine and cholinesterase inhibitors, Talanta, 65 (2005) 337-342. 

Fig. 37 (a) QD-based sensing of cocaine by the formation of a cocaine-aptamer supramolecular structure that triggers FRET and (b) time-dependent luminescence spectra of the system in the presence of cocaine. The inset shows a calibration curve for variable concentrations of cocaine and a fixed so observation time of 15 min. (c) Schematic of the FRET-based TNT sensor and (d) increase of the QD luminescence upon addition of TNT in the competitive assay format. (Reprinted with permission from [220, 221], Copyright 2009 Royal Society of Chemistry and 2005 American Chemical Society)... 

MB has been shown useful also for detection of cocaine by means of specific DNA aptamer [50]. The MB-tagged aptamer has been immobilized via thiol group onto a gold support. In absence of cocaine, the aptamer was partially unfolded. Addition of cocaine resulted in folding of aptamer into three-way junction, moving MB to a close proximity with the electrode surface. This resulted in an increase in reduction peak measured by AC voltammetry. Sensor was regenerable and allowed to detect cocaine within several seconds with sensitivity below 10pmol/L. 

Fig. 3 Electrochemical aptamer-based sensor of redox-tagged DNA against specific targets, (a) When the aptamer comes in contact with a small molecule, in this case cocaine, it folds, and the redox tag is brought closer to the electrode, increasing the current, (b) When the aptamer comes in contact with thrombin, the tag moves away from the surface, decreasing the electrochemical signal. Reproduced from [85] with permission. Copyright Langmuir, 2007...

Suleiman and Xu [128] described a novel reusable amperometric immuno-sensor for the determination of cocaine. Horseradish peroxidase and benzoylecgonine-antibody were co-immobilized on a chemically activated affinity membrane, which was then mounted over the tip of an oxygen electrode. The enzymatic electrocatalytic current response to the substrate is inhibited by the association of the antigen to the co-immobilized antibody. The calibration plot for cocaine was linear in the concentration range of lx 10 -1x10 M. 

Piezoelectric sensors have become a versatile tool in biosensorics to study protein-protein and protein-small molecule interactions. Here we present theoretical background on piezoelectric sensors and instructions, how to modify their surface with various recognition elements for cholinesterases. These recognition elements comprise an organophosphate (paraoxon), a cocaine derivative (BZE-DADOO), and a tricyclic, aromatic compound (propidium). Additionally, a guide to the kinetic evaluation of the obtained binding curves is given in this chapter. 

Some herbal treatments for cough contain local anesthetics that might act on nervous sensors in the mucosa of the pharynx and larynx before the medicine reaches the stomach. These include Erythroxylum coca (cocaine). Cannabis sativa (marijuana), and possibly Syzygium aromaticum (clove oil). However, there seems to be no evidence that these herbs have antitussive actions by this mechanism. Most local anesthetics also taste bitter, which could also have an antitussive action (see later). 

Stojanovic, M. N., de Prada, P., Landry, D. W. (2001). Aptamer-based folding fluorescent sensor for cocaine. J Am Chem Soc 123, 4928-4931. 

Baker, B. R., Lai, R. Y., Wood, M. S., Doctor, E. H., Heeger, A. J., Plaxco, K. W. (2006). An electronic, aptamer-based small-molecule sensor for the rapid, label-free detection of cocaine in adulterated samples and biological fluids. J Am Chem Soc 128, 3138-3139. 

Liu, J., Lu, Y. (2006). Fast colorimetric sensing of adenosine and cocaine based on a general sensor design involving aptamers and nanoparticles. Angew Chem Int Ed Engl 45, 90-94. 

The exciting properties of nucleic acids have opened new scenarios in the field of nanotechnology and sensor development. In particular, the dynamic properties of nucleic acids and the thermally indnced sequence-dependent separation of double-stranded DNA allow the utilization of nucleic acids with machinelike functions that can perform different motions or act as switches and motors (Beissenhirtz and Willner, 2006). The same principles have been applied for the development of aptamer-based machines, which can amplify the recognition event between the aptamer and the substrate through operation of the machine (Shlyahovsky et al., 2007). A scheme for the assay developed for cocaine is reported in Figure 8.10. 

An electronic, aptamer-based small-molecule sensor for the rapid, label-free detection of cocaine in adulterated samples and biological fluids. J Am Chem Soc 128, 3138-3139. 

QDs-based aptamer sensors were further developed by applying aptamer subunits that would self-assemble into supramolecular aptamer subunits-guest complexes in the presence of the analyte. CdSe/ZnS QDs were modifled with a subunit of the anti-cocaine aptamer (23), while the second aptamer subunit was functionalized with an acceptor dye (24). In the presence of a cocaine analyte, supramolecular complex formation occurred between the aptamer subunits and cocaine, which led to the FRET process between the QDs and the dye acceptor (Figure 6.21). 

J. Zhou, A.V. Ellis, H. Kobus, N.H. Voelcker, Aptamer sensor for cocaine using minor groove binder based energy transfer. Anal. Chim. Acta 719 (2012) 76-81. 

Owing to the broad spectrum of substrates for both enzymes, the sensor responds to various catecholamines, aminophenols and ferrocene derivatives. The best sensitivities were obtained for aminophenol and epinephrine where the lower limit of detection is 100 pM. The recycling sensor was used to trace the secretion of catecholamines in cultures of adrenal chromaffin cells. Furthermore both a sandwich assay for IgG and displacement of enzyme labeled cocaine have been indicated by the amplification enzyme sensor. 

Detection of Cocaine by Combining Conjugate Dispiacement and a Substrate-Recyciing-Sensor... 

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