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Hydrogels, water-filled networks that can adapt to external stimuli by altering their volume, are known for their high flexibility and biocompatibility. DNA, a critical biomolecule renowned for its exceptional characteristics including information transmission, molecular recognition, and editability, has found widespread applications in the biosensing field as well. The integration of these two biomaterials offers promising opportunities for the development of novel biosensors with enhanced sensitivity, specificity, and adaptability. Therefore, by virtue of the collective features, researchers have recently focused on the construction of responsive DNA hydrogel systems. This feature article describes recent developments in fabricating DNA hydrogels and their applications in the biosensing area. Initially, it focuses on the design strategies employed in preparing DNA hydrogels, encompassing both pure DNA hydrogels and hybridized DNA hydrogels. Subsequently, it summarizes the use of DNA hydrogels in biosensing applications, highlighting their applications in visual detection, electrochemical sensing, and optical biosensing analyses. Furthermore, the underlying responsive mechanisms within these biosensing systems are also described. Lastly, this article presents a comprehensive discussion on the existing challenges and prospects of responsive DNA hydrogels, offering insights into their potential to revolutionize the field of biosensing.

To detect biomarkers in complex samples, it is fundamental to avoid the nonspecific adsorption of impurities to improve the selectivity of biosensors. In this study, a sensitive antifouling electrochemiluminescence biosensor was proposed based on bovine serum albumin (BSA)- and exonuclease III (Exo III)-mediated nucleic acid cycle signal amplification strategy. Ti 3 C 2 T x -NH 4 , which has a large surface area and high metal conductivity, was crosslinked with BSA to improve the conductivity of the sensing interface, which shows antifouling performance excellently due to the electrical neutrality and good hydrophilicity of BSA hydrogel. The cyclic amplification strategy based on Exo III and DNA hybridization chain reaction significantly amplified the electrochemiluminescence signal and improved the sensitivity of p53 gene detection. The linear range of the biosensor is 1 fM-1 nM with a detection limit of 0.26 fM. More importantly, the sensor showed excellent selectivity when it was used to detect the p53 gene in real samples, such as serum. Thus, this unique antifouling sensing interface is expected to construct various electrochemical biosensors in clinical diagnosis and biopathological analysis.

A unique electrochemical sensor was constructed based on designed peptide hydrogels loaded with ciprofloxacin and gold nanoparticles, which exhibited excellent biocompatibility, antibacterial capability and electrochemical catalytic property. The peptide hydrogel was prepared base on the self-assembly of a designed short peptide sequence of Phe-Glu-Lys-Phe (FEKF) with the N-terminal modified with a fluorene methoxycarbonyl (Fmoc) group. The peptide hydrogel possessed nanofibrous network structure and exhibited good shear-thinning behavior and excellent biocompatibility, and it can be easily doped with gold nanoparticles and the antibiotic drug ciprofloxacin. The loaded antibacterial drug offered remarkable antibacterial activity of the hydrogel, while the loaded gold nanoparticles rendered the hydrogel excellent electrochemical catalytic capability towards the detection of a typical neurotransmitter dopamine. The combination of the antibacterial property and the electrochemical catalytic ability within a peptide hydrogel ensured the development of sensitive and antibacterial electrochemical sensors, and this strategy was expected to promote the construction of implantable sensors without infection., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2021 Elsevier B.V. All rights reserved.)

We designed a dual-color fluorescent nanoprobe for simultaneous detection and imaging of adenosine triphosphate and glutathione in living cells based on porous carbon nanospheres and a DNA hybrid hydrogel. Due to the non-template synthesis process and good biocompatibility, the nanohydrogel displayed a short preparation time and anti-nonspecific adsorption.

Herein, we have designed bifunctional composite nanospheres for carcinoembryonic antigen (CEA) sensing and targeted drug delivery, based on carbon dot loaded silica nanoparticles coated with DNA-cross-linked hydrogels. As a result, highly sensitive and selective CEA detection was achieved in vitro, and an effective cytotoxic effect was realized in vivo after loading doxorubicin.

Herein, we synthesized a kind of conductive supramolecular polymer hydrogel (CSPH) based on polyaniline (PANI) which can not only improve the conductivity but also promote antifouling performance of the aptasensor for the specific recruitment of thrombin (TB) from complex samples. With the electrochemical copolymerization of aniline (AN) and 3-aminophenylboronic acid (ABA) on glassy carbon electrode (GCE), the electrode was then inserted into the polyvinyl alcohol (PVA) solution to obtain robust CSPH through boric acid groups incorporated onto PANI to cause gelation of PVA solution, owing to the hydrophilicity of CSPH and nearly electrical neutrality, the modified electrode is antifouling without integration of other antifouling materials. A sandwich-type electrochemical aptasensor was constructed on the CSPH based electrode interfaces. Thrombin aptamer 1 (TBA1) were modified on the CSPH through amide bond, and thrombin aptamer 2 modified magnetic nanoparticles (MNP-TBA2) are used as signal amplification probes, the aptasensor has good sensitivity with a linear range from 1 pmol/L to 10 nmol/L and has a detection limit down to 0.64 pmol/L. The strategy of utilizing eletropolymerization of CSPH films to undergo highly selective thrombin recognition is, of course, readily extended to a broad range of targets in the real samples, and the recovery was ranging from 95.2% to 106.3% and RSDs varying from 2.3% to 4.5%., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Herein, we have designed a ratiometric fluorescent nanoprobe for adenosine triphosphate sensing and imaging in living cells, based on silica nanoparticles and a DNA-functionalized hybrid hydrogel. This ratiometric detecting method could validly avoid false-positive signals. Due to its controllable size, favorable biocompatibility and biostability, the nanohydrogel exhibited high cellular permeability and fast response in living cells.

A sensitive and reliable bimodal electrochemiluminescent (ECL) system based on CdTe quantum dots (QDs) and luminol as double luminophores is constructed. CdTe QDs tagged with the aptamer (CdTe-Apt 2) of cancer cells are used as the detection signals, while luminol molecules are used as internal standards. The electrodeposited polyaniline-based conducting polymer hydrogel (CPH) on the electrode surfaces improves the biocompatibility and conductivity of the sensing interfaces effectively. Furthermore, electron transfer is probably much easier when luminol and coreactant potassium persulfate (K 2 S 2 O 8 ) are immobilized in the CPH in comparison to that in solution. Cancer cells are captured to the electrode surface by another aptamer linked to the Au nanoparticles immobilized in the CPH through Au-S bonds. In the developed bimodal ECL system, an internal standard method is used to quantify cancer cells by comparing the differences in sensitivity of the double-peak ECL signals with that of target analytes. The internal standard method of ECL strategy can provide very accurate detection results in a complex environment because interferences in the system can be eliminated through the self-calibration of two emission spectra. A linear relation is found on the basis of a plot of the ΔECL CdTe /ΔECL luminol against the concentration of cancer cells within 100-6500 cells mL -1 under optimized conditions. The developed ratiometric ECL cytosensor with internal standard can significantly improve the accuracy and reliability of cell assays in complex biological media, demonstrating promising applications in healthcare monitoring and clinical diagnostics.

Electrochemical biosensors are suitable for trace detection of biomarkers in serum due to their high sensitivity and fast response time. However, the extensive adsorption of non-specific biomolecules may affect detection results and reduce the operating life of sensors. Herein, an efficient electrochemical biosensor based on double-conductive antifouling hydrogel was developed for ultrasensitive detection of carcinoembryonic antigen (CEA) in serum. Specifically, the antifouling hydrogel was designed with MXene as the conductive framework, and its inherent surface hydrophilicity made it have good antifouling ability. Meanwhile, the introduction of conductive poly(3,4-ethylenedioxythiophene)-poly(styrenesulfonate) further improved the conductivity and stability and of antifouling hydrogel. Furthermore, the prepared MXene nanosheets exhibited large surface area, which could load a large amount of [Ru(NH 3) 6 ]3+ as internal standards. Importantly, the encapsulation of [Ru(NH 3) 6 ]3+ in hydrogel can not only eliminate the environmental and instrument errors, but also realize the integration of antifouling and internal standards, thus simplifying the construction process and improving the detection accuracy of the biosensor. Based on this, the proposed signal "on-off" electrochemical antifouling biosensor realized trace detection of CEA in a wide linear range (1 pg/mL ∼ 1 μg/mL), with a detection limit as low as 0.41 pg/mL (3 δ/k). This study broadens the application of hydrogels in electrochemical antifouling systems, providing a positive reference for sensitive and accurate determination of biomarkers in serum samples. • Developing a double-conductive antifouling hydrogel for electrochemical analysis. • The prepared antifouling hydrogel improves the specificity and operating life of the biosensor. • The integration of antifouling and ratio improves detection sensitivity and accuracy. • The proposed antifouling biosensor is expected to realize trace detection of serum biomarkers. [ABSTRACT FROM AUTHOR]

The tremendous morbidity and mortality caused by bacterial infections have emerged as a formidable menace to human health. The early detection and treatment of bacterial infections is imperative for effectively managing the progression of infectious diseases and mitigating infection-related mortality. In this study, we constructed a nanohydrogel consisting of cationic zinc phthalocyanine (CZP) and hyaluronic acid, which was further functionalized with a novel β-galactosidase detection probe, resulting in the formation of product CZP@HA:probe. The release of CZP and probe from CZP@HA:probe can be triggered by hyaluronidase, and the fluorescence of CZP and probe was turned on successively by hyaluronidase and β-galactosidase, respectively, demonstrating the dual enzyme-responsive property of CZP@HA:probe. CZP@HA:probe exhibited potent photodynamic killing activity against bacteria. The antibacterial mechanism potentially involved the generation of reactive oxygen species within bacteria and the disruption of the bacterial outer membrane. CZP@HA:probe had significant efficacy in promoting wound healing and exhibited a fluorescent indication of wound infections. The construction strategy of the nanohydrogel can be applied to other photosensitizers and probes, offering a novel perspective for the detection and treatment of bacterial infections. [Display omitted] • A simple and effective method to construct a nanohydrogel for detection and treatment of bacterial infections. • Hyaluronidase-triggered cargo release from nanohydrogels, double-enzyme cascade-responsive property for bacterial detection. • The nanohydrogels possess significant bacteria-targeting property and exhibit excellent photodynamic bactericidal efficacy. • The nanohydrogels possessed a significant capacity to effectively facilitate the healing process of infected wounds. [ABSTRACT FROM AUTHOR]

Recently, rapid acquisition of bacterial resistance and consequent slow healing of infected wounds threaten human life and health. In this study, chitosan-based hydrogels and nanocomplexes ZnPc(COOH) 8 :PMB composed of photosensitizer ZnPc(COOH) 8 and antibiotic polymyxin B (PMB) were integrated into a thermosensitive antibacterial platform ZnPc(COOH) 8 :PMB@gel. Interestingly, fluorescence and reactive oxygen species (ROS) of ZnPc(COOH) 8 :PMB@gel can be triggered by E. coli bacteria at 37 °C, but not by S. aureus bacteria, which gave the potential to simultaneously detect and treat Gram-negative bacteria. The survival rate for a certain amount of E. coli bacteria treated with ZnPc(COOH) 8 :PMB (ZnPc(COOH) 8 2 μM) was decreased by approximately fivefold than that with either ZnPc(COOH) 8 or PMB alone, indicating combined antibacterial efficacy. ZnPc(COOH) 8 :PMB@gel facilitated the complete healing of wounds infected with E. coli bacteria in about seven days, while over 10 % wounds treated with ZnPc(COOH) 8 or PMB remained unhealed on the 9th day. ZnPc(COOH) 8 :PMB resulted in a threefold increase of ZnPc(COOH) 8 fluorescence in E. coli bacteria suggesting enhanced uptake of ZnPc(COOH) 8 for the intervention of PMB on membrane permeability. The construction principle of the thermosensitive antibacterial platform and the combined antimicrobial strategy can be applied to other photosensitizers and antibiotics for detection and treatment of wound infections. [ABSTRACT FROM AUTHOR]