A dye-sensitized solar cell acting as the electrical reading box of an immunosensor: Application to CEA determination

New autonomous and self-signaling biosensing device for sarcosine detection

An early diagnosis is the gold standard for cancer survival. Biosensors have proven their effectiveness in monitoring cancer biomarkers but are still limited to a series of requirements. This work proposes an integrated power solution, with an autonomous and self-signaling biosensing device. The biorecognition element is produced in situ by molecular imprinting to detect sarcosine, a known biomarker for prostate cancer. The biosensor was assembled on the counter-electrode of a dye-sensitized solar cell (DSSC), simultaneously using EDOT and Pyrrole as monomers for the biomimetic process and the catalytic reduction of triiodide in the DSSC. After the rebinding assays, the hybrid DSSC/biosensor displayed a linear behavior when plotting the power conversion efficiency (PCE) and the charge transfer resistance (R_CT) against the logarithm of the concentration of sarcosine. The latter obtained a sensitivity of 0.468 Ω/decade of sarcosine concentration, with a linear range between 1 ng/mL and 10 μg/mL, and a limit of detection of 0.32 ng/mL. When interfacing an electrochromic cell, consisting of a PEDOT-based material, with the hybrid device, a color gradient between 1 ng/mL and 10 μg/mL of sarcosine was observed. Thus, the device can be used anywhere with access to a light source, completely equipment-free, suitable for point-of-care analysis and capable of detecting sarcosine within a range of clinical interest.

Single Molecule Level and Label-Free Determination of Multibiomarkers with an Organic Field-Effect Transistor Platform in Early Cancer Diagnosis

The single molecule level determination with a transistor (SiMoT) platform has attracted considerable attention in the recognition of various ultralow abundance biomolecules, while complicated labeling and testing processes limit its further applications. Recently, organic field-effect transistor (OFET)-based biosensors are good candidates for constructing an advanced label-free SiMoT platform due to their facile fabrication process, rapid response time, and low sample volume with a wide range of detection. However, the sensitivity of most OFET-based biosensors is in the order of nM and pM, which cannot meet the detection requirements of ultralow abundance protein. Herein, a label-free SiMoT platform is demonstrated by integrating pillar[n]arene as a signal amplifier, and the detection limit can reach 4.75 aM. Besides, by simultaneous determination of α-fetoprotein, carcinoembryonic antigen, and prostate antigen, the proposed multiplexed OFET-based SiMoT platform provides a key step in reliable early cancer diagnosis.

A Colorimetric Ag+ Probe for Food Real-Time Visual Monitoring

Monitoring food quality throughout the food supply chain is critical to ensuring global food safety and minimizing food losses. Here we find that simply by mixing an aqueous solution of sugar-stabilized Ag+ and amines in an open vessel leads to the generation of Ag NPs and an intelligent evaluation system based on a colorimetric Ag+ probe is developed for real-time visual monitoring of food freshness. The self-assembly reaction between methylamine (MA) generated during meat storage and the colorimetric Ag+ probe produces different color changes that indicate changes in the quality of the meat. The colorimetric Ag+ probe was integrated into food packaging systems for real-time monitoring of chilled broiler meat freshness. The proposed evaluation system provides a versatile approach for detecting biogenic amines and monitoring chilled broiler meat freshness and it has the advantages of high selectivity, real-time and on-site measurements, sensitivity, economy, and safety and holds great public health significance.

Potentiometric Biosensor Based on Artificial Antibodies for an Alzheimer Biomarker Detection

This paper presents a potentiometric biosensor for the detection of amyloid β-42 (Aβ-42) in point-of-care analysis. This approach is based on the molecular imprint polymer (MIP) technique, which uses covalently immobilised Aβ-42 to create specific detection cavities on the surface of single-walled carbon nanotubes (SWCNTs). The biosensor was prepared by binding Aβ-42 to the SWCNT surface and then imprinting it by adding acrylamide (monomer), N,N’-methylene-bis-acrylamide (crosslinker) and ammonium persulphate (initiator). The target peptide was removed from the polymer matrix by the proteolytic action of an enzyme (proteinase K). The presence of imprinting sites was confirmed by comparing a MIP-modified surface with a negative control (NIP) consisting of a similar material where the target molecule had been removed from the process. The ability of the sensing material to rebind Aβ-42 was demonstrated by incorporating the MIP material as an electroactive compound in a PVC/plasticiser mixture applied to a solid conductive support of graphite. All steps of the synthesis of the imprinted materials were followed by Raman spectroscopy and Fourier transform infrared spectroscopy (FTIR). The analytical performance was evaluated by potentiometric transduction, and the MIP material showed cationic slopes of 75 mV-decade−1 in buffer pH 8.0 and a detection limit of 0.72 μg/mL. Overall, potentiometric transduction confirmed that the sensor can discriminate Aβ-42 in the presence of other biomolecules in the same solution.

Facile Functionalization Strategy for Ultrasensitive Organic Protein Biochips in Multi-Biomarker Determination

In recent years, organic field-effect transistors (OFETs) have shown great potential for advanced protein biochips due to their inherent biocompatibility and high-throughput detectability. However, the development of OFET-based protein biochips is still at an early stage. On the one hand, single-biomarker determination is not sufficient for the diagnosis of cancer; thus, simultaneous monitoring of electrical signals toward multi-biomarkers is widely concerned and explored. On the other hand, an optimized functionalization strategy for efficient protein immobilization is another key to make OFET-based protein biochips accessible with improved detection performance. Herein, a facile functionalization strategy is developed for excellent charge-transport thin films by suppressing the gelation of diketopyrrolopyrrole (DPP)-based polymer semiconductors with the addition of the glutaraldehyde cross-linking agent. Besides, functional groups are introduced on the device surface for efficient attachment of antibodies as receptors via a condensation reaction, enabling simultaneous determination of α-fetoprotein biomarker and carcinoembryonic antigen biomarker with improved sensitivity and reliability. Therefore, the proposed high-throughput OFET-based protein biochip has the potential to be widely utilized in early liver cancer diagnosis.

A passive direct methanol fuel cell as transducer of an electrochemical sensor, applied to the detection of carcinoembryonic antigen

This work describes an electrochemical sensor with a biomimetic plastic antibody film for carcinoembryonic antigen (CEA, an important biomarker in colorectal cancer), integrated in the electrical circuit of a direct methanol fuel cell (DMFC), working in passive mode and used herein as power supply and signal transducer. In detail, the sensing layer for CEA consisted of a Fluorine-doped Tin Oxide (FTO) conductive glass substrate - connected to the negative pole side of the DMFC - with a conductive poly (3,4-ethylenedioxythiophene) (PEDOT) layer and a polypyrrol (PPy) molecularly-imprinted polymer (MIP), assembled in-situ. This sensing element is then closed using a cover FTO-glass, hold in place with a clip, connected to the positive side of the DMFC. When compared with control DMFCs, the power curves of DMFC/Sensor integrated system showed decreased power values due to the MIP layer interfaced in the electrical circuit, also displaying high stability signals. The DMFC/Sensor was further calibrated at room temperature, in different medium (buffer, a synthetic physiological fluid model and Cormay® serum), showing linear responses over a wide concentration range, with a limit of detection of 0.08 ng/mL. The DMFC/Sensor presented sensitive data, with linear responses from 0.1 ng/mL to 100 μg/mL and operating well in the presence of human serum. Overall, the results obtained evidenced the possibility of using a DMFC as a transducing element in an electrochemical sensor, confirming the sensitive and selective readings of the bio (sensing) imprinted film. This integration paves the way towards fully autonomous electrochemical devices, in which the integration of the sensor inside the fuel cell may be a subsequent direction.

Self-powered and self-signalled autonomous electrochemical biosensor applied to cancinoembryonic antigen determination

This work describes a novel and disruptive electrochemical biosensing device that is self-powered by light and self-signalled by an optical readout. Electrical energy requirements are ensured by a photovoltaic cell that is a dye sensitized solar cell (DSSC), in which one of the electrodes is the biosensing unit. The readout converts electrical energy into colour by an electrochromic cell and signals the concentration dependent event. This device was designed to target a cancer biomarker, cancinoembryonic antigen (CEA). In brief, the sensing unit was assembled on a conductive glass substrate with a highly conductive poly(3,4-ethylenedioxythiophene) (PEDOT) layer, using a molecularly-imprinted polymer of polypyrrol (PPy) as biorecognition element. This sensing unit acted as the counter electrode (CE) of the DSSC, generating a hybrid device with a maximum power conversion efficiency of 3.45% for a photoanode area of 0.7 cm². The hybrid DSSC/biosensor had an electrical output that was CEA concentration dependent from 100 ng/mL to 100 μg/mL, with a limit detection of 0.14 ng/mL in human urine samples. The electrochromic cell consisted of a PEDOT-based material and showed a colour gradient change for CEA concentrations, ranging from 0.1 ng/mL to 100 μg/mL. Overall, this self-powered and self-signalled set-up is equipment free and particularly suitable for point-of-care analysis (POC), being able to screen CEA in real samples and differentiating critical concentrations for establishing a diagnosis. It holds the potential to provide clinical relevant data anywhere, in a fully independent manner.

Photovoltaics, plasmonics, plastic antibodies and electrochromism combined for a novel generation of self-powered and self-signalled electrochemical biomimetic sensors

This work describes further developments into the self-powered and self-signalled biosensing system that merges photovoltaic cells, plastic antibodies and electrochromic cells into a single target. Herein, the plasmonic effect is introduced to improve the photoanode features of the photovoltaic cell, a dye sensitized solar cell (DSSC), and better electrocatalytic features are introduced in the electrode containing the sensing element. In brief, the DSSC had a counter-electrode of poly(3,4-ethylenedioxythiophene) on an FTO glass modified by a plastic antibody of 3,4-ethylenedioxythiophene and pyrrol. The photoanode had dye sensitized TiO₂ modified with gold nanoparticles (AuNPs) to increase the cell efficiency, aiming to improve the sensitivity of the response of hybrid device for the target biomarker. The target biomarker was carcinoembryonic antigen (CEA). The response of the hybrid device evidenced a linear trend from 0.1 ng/mL to 10 μg/mL, with an anionic slope of 0.1431 per decade concentration. The response of the plastic antibody for CEA revealed great selectivity against other tumour markers (CA 15-3 or CA 125). The colour response of the electrochromic cell was also CEA concentration dependent and more sensitive when the hybrid device was set-up with a photoanode with AuNPs. A more intense blue colour was obtained when higher concentrations of CEA were present. Overall, this improved version of the self-powered and self-signalled set-up has zero-requirements and is particularly suitable for point-of-care analysis (POC). It is capable of screening CEA in real samples and differentiating clinical levels of interest. This concept opens new horizons into the current cancer screening approaches.

Amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 based on dye sensitization of the semiconductor composite C3N4-MoS2

The authors describe an amplified photoelectrochemical immunoassay for the tumor marker carbohydrate antigen 724 (CA724). The method employs a C₃N₄-MoS₂ semiconductor as the photoelectric conversion layer. The nanocomposite was characterized by transmission electron microscopy, Fourier transform infrared spectroscopy, X-ray powder diffraction, and UV-vis diffuse reflectometry. The dye eosin Y was encapsulated into CaCO₃ nanospheres which then were used as labels for antibody against CA724. In addition, Fe₃O₄ nanospheres were employed as magnetic platform for constructing photoelectrochemical sandwich immunoassay. The CaCO₃ nanospheres can be dissolved with aid of ethylene diamine tetraacetic acid (EDTA) and the carried eosin Y in CaCO₃ is released. The released dyes sensitizes the C₃N₄-MoS₂ semiconductor, which induces photocurrent amplification. Under optimal conditions and at a typical working voltage of 0 V (vs. SCE), the photocurrent increases linearly in the range of 0.05 mU mL^-1 to 500 mU mL^-1 of CA724, with a 0.02 mU mL^-1 detection limit. Graphical abstract The C₃N₄-MoS₂ complex, with high efficiency of electron transport, was synthesized to construct a photoelectrochemical analytical platform. A sandwich-type immunoassay was established on the surface of magnetic beads. Carbohydrate antigen 724 in sample was detected sensitively by using sensitization of released eosin Y as signal amplifiery.