Probing charge transfer through antifouling polymer brushes by electrochemical methods: The impact of supporting self-assembled monolayer chain length

Ultrathin surface-tethered polymer brushes represent attractive platforms for a wide range of sensing applications in strategically vital areas such as medicine, forensics, or security. The recent trends in such developments towards "real world conditions" highlighted the role of zwitterionic poly(carboxybetaine) (pCB) brushes which provide excellent antifouling properties combined with bio-functionalization capacity. Highly dense pCB brushes are usually prepared by the "grafting from" polymerization triggered by initiators on self-assembled monolayers (SAMs). Here, multi-methodological experimental studies are pursued to elucidate the impact of the alkanethiolate SAM chain length (C6, C8 and C11) on structural and functional properties of antifouling poly(carboxybetaine methacrylamide) (pCBMAA) brush. Cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS) in a custom-made 3D printed cell employing [Ru(NH3)6]3+/2+ redox probe were used to investigate penetrability of SAM/pCBMAA bilayers for small molecules and interfacial charge transfer characteristics. The biofouling resistance of pCBMAA brushes was characterized by surface plasmon resonance; ellipsometry and FT-IRRAS spectroscopy were used to determine swelling and relative density of the brushes synthesized from initiator-bearing SAMs with varied carbon chain length. The SAM length was found to have a substantial impact on all studied characteristics; the highest value of charge transfer resistance (Rct) was observed for denser pCBMAA on longer-chain (C11) SAM when compared to shorter (C8/C6) SAMs. The observed high value of Rct for C11 implies a limitation for the analytical performance of electrochemical sensing methods. At the same time, the pCBMAA brushes on C11 SAM exhibited the best bio-fouling resistance among inspected systems. This demonstrates that proper selection of supporting structures for brushes is critical in the design of these assemblies for biosensing applications.

Advances in the Determination of Anabolic-Androgenic Steroids: From Standard Practices to Tailor-Designed Multidisciplinary Approaches

Anabolic-androgenic steroids (AASs), a group of compounds frequently misused by athletes and, unfortunately, also by the general population, have lately attracted global attention; thus, significant demands for more precise, facile, and rapid AAS detection have arisen. The standard methods ordinarily used for AAS determination include liquid and gas chromatography coupled with mass spectrometry. However, good knowledge of steroid metabolism, pretreatment of samples (such as derivatization), and well-trained operators of the instruments are required, making this procedure expensive, complicated, and not routinely applicable. In the drive to meet current AAS detection demands, the scientific focus has shifted to developing novel, tailor-made approaches leading to time- and cost-effective, routine, and field-portable methods for AAS determination in various matrices, such as biological fluids, food supplements, meat, water, or other environmental components. Therefore, herein, we present a comprehensive review article covering recent advances in AAS determination, with a strong emphasis on the increasingly important role of chemically designed artificial sensors, biosensors, and antibody- and fluorescence-based methods.

Probing polymer brushes with electrochemical impedance spectroscopy: a mini review

Polymer brushes are frequently used as surface-tethered antifouling layers in biosensors to improve sensor surface-analyte recognition in the presence of abundant non-target molecules in complex biological samples by suppressing nonspecific interactions. However, because brushes are complex systems highly responsive to changes in their surrounding environment, studying their properties remains a challenge. Electrochemical impedance spectroscopy (EIS) is an emerging method in this context. In this mini review, we aim to elucidate the potential of EIS for investigating the physicochemical properties and structural aspects of polymer brushes. The application of EIS in brush-based biosensors is also discussed. Most common principles employed in these biosensors are presented, as well as interpretation of EIS data obtained in such setups. Overall, we demonstrate that the EIS-polymer brush pairing has a considerable potential for providing new insights into brush functionalities and designing highly sensitive and specific biosensors.

Stanazolol derived ELISA as a sensitive forensic tool for the detection of multiple 17α-methylated anabolics

Two valuable forensic tools based on enzyme-linked immunoassays (ELISAs) for the analysis of 17α-methylated steroids were developed using haptens of stanazolol and its conjugates with biotin. Haptens containing terminal carboxylic group were conjugated to bovine serum albumin (BSA), rabbit serum albumin (RSA) or ovalbumin (OVA). Eight batches of antisera (RAbs) obtained by immunization of rabbits were tested in an indirect competitive ELISA system using immobilization of RSA conjugate (RSA/hapten) and competitor immobilization of the biotinylated conjugate (AB-ELISA) to avidin (avidin/hapten). The best results were achieved with the RAb 212 antibodies in RSA/ST-3 and avidin/ST-10 assembled variants. For the RSA/ST-3 system, an IC₅₀ of 0.3 ng/mL and a detection limit of 0.02 ng/mL were measured. In case of avidin/ST-10 variant, IC₅₀ was of 3.9 ng/mL and a detection limit of 0.57 ng/mL were obtained. The effect of solvent was tested as well as the stability of coated microtiter plates over four-month period. The cross-reactivity of the developed assays with other anabolic steroids was tested and high sensitivity towards 17α-methylated steroids was observed. RSA/ST-3 assay showed significant cross-reactivity with 17α-methyltestosterone (81.2%), oxymetholone (30.4%), methandienone (10.0%) and methyl dihydrotestosterone (7.7%). Similarly, in the avidin/ST-10 assay, 17α-methyltestosterone (34.5%), mestanolone (32.1%), oxymetholone (22.7%), methandienone (14.2%), 9-dehydromethyltestosterone (12.5%) and oxandrolone (1.2%) exhibited high cross-reactivity. The functionality of the developed systems was verified by the successful identification of a series of 17α-methylated anabolic steroids in a set of real samples including pharmaceutical preparations seized by the Police of the Czech Republic on the black market.

(1S,2S)-Cyclohexane-1,2-diamine-based Organosilane Fibres as a Powerful Tool Against Pathogenic Bacteria

An urgent need to find an effective solution to bacterial resistance is pushing worldwide research for highly effective means against this threat. Newly prepared hybrid organosilane fibres consisting of a (1S,2S)-cyclohexane-1,2-diamine derivative, interconnected in the fibre network via covalent bonds, were fully characterised via different techniques, including FTIR, TGA-FTIR, SEM-EDS, and solid-state NMR. Fibrous samples were successfully tested against two types of pathogenic bacterial strains, namely Staphylococcus aureus, and Pseudomonas aeruginosa. The obtained results, showing >99.9% inhibition against Staphylococcus aureus and Pseudomonas aeruginosa in direct contact compared to the control, may help particularly in case of infections, where there is an urgent need to treat the infection in direct contact. From this point of view, the above-mentioned fibrous material may find application in wound healing. Moreover, this new material has a positive impact on fibroblasts viability.

Two immunoassays for the detection of 2C-B and related hallucinogenic phenethylamines

INTRODUCTION

The use of new psychoactive substances as drugs of abuse has dramatically increased over the last years. Hallucinogenic phenethylamines gained particular popularity as they have both stimulating and psychedelic effects. Although generally perceived as safe, these illicit drugs pose a serious health risk; they have been linked to cases of severe poisoning or even deaths. Therefore, simple, cost-effective and reliable methods are needed for rapid determination of abused hallucinogens.

METHODS

For this purpose, two haptens derived from 2C-H were designed, synthesized and subsequently attached to a carrier protein. Polyclonal antibodies obtained from a rabbit immunized with one of the prepared immunogens were used for the development of two immunoassays.

RESULTS

In this study, a lateral flow immunoassay (LFIA) and an enzyme linked immunosorbent assay (ELISA) for the detection of 2C-B and related hallucinogenic phenethylamines in urine were developed. The presented LFIA is primarily suitable for on-site monitoring as it is simple and can provide a visual evidence of 2C-B presence within a few minutes. Its reasonable sensitivity (LOD_LFIA = 15 ± 7 ng mL^-1) allows detection of the drug presence in urine after acute exposure. For greater accuracy, highly sensitive ELISA (LOD_ELISA = 6 ± 3 pg mL^-1) is proposed for toxicological quantitative analyses of positive samples captured by the LFIA.

DISCUSSION

The comparison of the ELISA with the well-established UHPLC-MS-MS method shows excellent agreement of results, which confirms good potential of the ELISA to be used for routine analyses of 2C-B and related hallucinogenic phenethylamines of both main sub-families.

Sensitive enzyme immunoassay for screening methandienone in dietary supplements

Methandienone is a synthetic exogenous steroid which, like other anabolic steroids, is strictly regulated in many countries. In recent years, increasing numbers have been detected of illegal additions into dietary supplements of methandienone and other anabolic androgenic steroids (AAS). In this work, a competitive indirect enzyme-linked immunosorbent assay (ELISA) has been constructed for the detection of methandienone using an antiserum against methandienone. Under optimal experimental conditions, the ELISA achieved a limit of detection of 0.04 ± 0.01 µg.g^-1. The obtained intra- and inter-day coefficients of variation were less than 8%. The developed ELISA was applied in the analysis of real dietary supplement samples. To minimise the effect of the sample matrix, the sample extracts were simply diluted before addition into the immunoassay. The achieved recovery values were around 100%. Results obtained from the ELISA correlated well, both in terms of accuracy and precision, with those obtained by UHPLC-MS/MS (reference method). The presented ELISA could be successfully applied for the simple screening of dietary supplements.

Use of novel haptens in the production of antibodies for the detection of tryptamines

Tryptamines are a group of hallucinogenic drugs whose detection in body fluids could be simplified by immunochemical assay kits. Antibodies for these assays are obtained by the immunization of laboratory animals with conjugates of a hapten similar to the target analyte and a suitable protein. Therefore we synthesized novel haptens derived from tryptamine-based drugs, with N,N-dimethyltryptamine (DMT), 5-methoxy-N,N-dimethyltryptamine (5-MeO-DMT) and N,N-diisopropyltryptamine (DiPT) selected as the target analytes. Their structures were modified with a short linker ended with a carboxylic group. The haptens were conjugated with bovine serum albumin (BSA) and rabbits were immunized with the conjugates. The obtained polyclonal antibodies showed good reactivity and the LOD of the constructed ELISAs was in the range 0.006–0.254 ng mL⁻¹. Thus, they are suitable for the development of immunochemical assay kits.

We synthesized haptens derived from tryptamine-based drugs and used them in the production of antibodies against various tryptamines.

Lateral flow immunoassay and enzyme linked immunosorbent assay as effective immunomethods for the detection of synthetic cannabinoid JWH-200 based on the newly synthesized hapten

In recent years, the use of synthetic cannabinoids (SCs) as drugs of abuse has greatly increased. SCs are associated with a risk of severe poisoning or even death. Therefore, more rapid, cost effective and reliable methods are needed, especially for the screening of drivers after traffic accidents and for detailed toxicological analysis in forensic laboratories. In this study, we developed a lateral flow immunoassay (LFIA) and an enzyme linked immunosorbent assay (ELISA) for the detection of JWH-200 in oral fluids. For this purpose a new hapten was prepared using a ten-step synthetic route. The developed immuno methods are based on antibodies obtained from rabbit immunized with synthesized hapten conjugated to carrier protein. The proposed methods are highly sensitive (LOD_LFIA = 0.08 ± 0.04 ng mL^-1; LOD_ELISA = 0.04 ± 0.02 ng mL^-1). They were applied to the quantification of JHW-200 in spiked oral fluids. The recoveries ranged from 82 to 134% for both methods. The results correlated excellently with results obtained using UHPLC-MS/MS (R²_LFIA = 0.99; R²_ELISA = 0.99). Our developed methods could be an important tool for analyses of JWH-200 in human oral fluids. The one-step LFIA is particularly suitable for roadside and on-site monitoring due to the rapid qualitative results it delivers, while the ELISA is especially useful for laboratory quantitative analyses of positive samples captured by LFIA.