P3HT-PbS nanocomposites with mimicking enzyme as bi-enhancer for ultrasensitive photocathodic biosensor

https://doi.org/10.1016/j.bios.2021.113806Get rights and content

Highlights

  • The p-typed P3HT could be sensitized by PbS dots , providing a high charge mobility and strong photosensitivity.

  • The hemin/G-quadruplexes could accelerate the generation of electron acceptor O2 in the assistant of H2O2.

  • Hemin/G-quadruplexes inherited the HRP mimicking catalytic capability that further improved the produce of plentiful O2.

  • The cathode signal was enhanced significantly to improve the detection sensitivity and extend the detection range.

Abstract

Photocathodic biosensor has great capability in anti-interference from reductive substances, however, the low signal intensity of photoactive species with inferior detection sensitivity restricts its wide application. In this work, the P3HT-PbS nanocomposites were synthesized as signal tags, by integrating with target-trigger generated hemin/G-quadruplex nanotail as bi-enhancer to significantly apmplify the photocurrent, an ultrasensitive photocathodic biosensor was proposed for detection of β2-microglobulin (β2-MG). Impressively, P3HT with cathode signal is an attractive polymer consisted of substantial thiophene groups with high absorption coefficient and mobility of photo-generated holes, which could anchor with the PbS dots as sensitizer, providing a high charge mobility and strong photosensitivity. More importantly, target-trigger generated hemin/G-quadruplexes could accept the electron from illuminated photoactive species through the conversion of Fe(III)/Fe(II) in hemin, effectively reducing charge recombination rate as well as accelerating the generation of electron acceptor O2 in the assistant of H2O2. Moreover, hemin/G-quadruplexes inherited the HRP mimicking catalytic capability that further improved the produce of plentiful O2. As a result, PEC cathode signal was significantly enhanced for sensitive analysis of β2-MG protein with a good detection range of 0.1 pg/mL to 100 ng/mL. It would provide a path for establishing PEC platform with excellent anti-interference ability and extend the application of photoelectrochemical (PEC) biosensor in bioanalysis and early disease diagnosis.

Introduction

Cathode photoelectrochemical (PEC) biosensor as an emerging and promising technique has attracted considerable attention in bioassay application (Gong et al., 2016; Shi et al., 2018; Song et al., 2018). Since the photogenerated cathode response utilizes the holes as majority carriers, electron acceptor instead of electron donor is required at the electrolyte solution, which can effectively avoid competition influence of absorbed reductive interference in real sample with the merit of reduced false signal output (Bellani et al., 2019; Fan et al., 2016; Huang et al., 2015; Wang et al., 2018; Wu et al., 2018; Zhu et al., 2020). Nevertheless, photocathode owns a higher charge recombination rate rather than that of electron as majority carriers at photoanode, leading to an inferior photocurrent and detection sensitivity (Sun et al., 2017; Wang et al., 2019; Yan et al., 2015). The common approach that only relies on finite dissolved oxygen (DO) as electron acceptor for signal improvement severely restricts the development of cathode PEC biosensor (Y. Wang et al., 2018; Yang and Moon, 2019). Therefore, exploitation of novel cathode photoactive material with high photo-to-electric conversion efficiency and integration of effective amplification strategy are also virtue important.

Organic-inorganic nanocomposites inherit the advantages of organic high charge mobility and inorganic strong photosensitivity, in which the well-matched band gap would further improve the separation of photogenerated carrier (Feng et al., 2017; Grechko et al., 2018; Jiang et al., 2015; Singh et al., 2020). Still, the main problem for traditional hybrid nanocomposites is their poor compatibility between organic and inorganic phase that cause the compounding effect with low electron transfer efficiency (Hu et al., 2019; Ruan et al., 2021; Shaw et al., 2021). To address this issue, we here synthetized poly(3-hexylthiophene-2,5-diyl) (P3HT)-PbS hybrid sensitizer structure. P3HT is an attractive conjugated polymer and one of the most extensively π-conjugated polymer with high absorption coefficient and mobility of photo-generated holes. This structure is consisted of substantial thiophene groups, which could anchor with the functionalized sulfide inorganic material via interaction of disulfide bonds between P3HT polymer and sulfide. Therefore, p-type P3HT provides plentiful thiophene groups for simply anchoring PbS quantum dot for generation of P3HT-PbS hybrid composites. Through the dispersion of PbS dots within P3HT conjugated polymer, less macroscopic phase separation would efficiently shorten electron transfer distance and reduce energy loss to accelerate electron transport, which could employ as excellent photocathode photoactive material (Tang et al., 2018; Watts et al., 2019).

So far, cathode PEC biosensor remains deficiency in appropriate signal amplification strategy. The well-known hemin/G-quadruplex comprises a hemin and G-rich DNA sequence with peroxidase-like catalytic activity and desiring resistant to harsh environment (Aizen et al., 2015; Cao et al., 2020; Guo et al., 2017; Li et al., 2018; Liu et al., 2019; Lv et al., 2017; Wang et al., 2021). Different from most of works that heavily reliant on catalytic performance of hemin/G-quadruplex (Chen et al., 2021; Fu et al., 2021; Ge et al., 2020a, 2020b; Kong et al., 2019; Yin et al., 2018; Zhang et al., 2021; Zheng et al., 2021; Zhou et al., 2021; Zhu et al., 2021), in our work, hemin/G-quadruplexes as bi-enhancer for signal amplification was introduced to realize cathode signal amplification, which could accept electron from illuminated photoactive species through the conversion of Fe(III)/Fe(II) in hemin, thus significantly reducing charge recombination rate as well as accelerating the generation of electron acceptor O2 in the assistant of H2O2. Simultaneously, hemin/G-quadruplexes inherited the HRP mimicking catalytic capability that further improved the produce of plentiful O2 for further improving the photocurrent response.

Based on the observation mentioned above, here, organic-inorganic nanocomposites based sensitive cathode photoelectrochemical platform with mimicking enzyme hemin/G-quadruplexes as bi-enhancer was proposed for sensitive determination of β2-MG (Scheme 1). P3HT-PbS as substrate signal tag was coated on electrode with a relatively low initial PEC cathode signal at the electrolyte solution. After a typical sandwich immune reaction at the electrode, antibody labeled DNA would assemble to trigger the rolling circle amplification (RCA) for the abundant generation of hemin/G-quadruplexes. The hemin/G-quadruplexes long DNA tails as bi-enhancer could thus be acquired to significantly amplify photocathode signal for the sensitive detection. This proposed cathode PEC biosensor could efficiently avoid the influence of absorbed reductive substance and acquire true photocurrent response with the excellent anti-interference. Combing with the effective DNA amplification strategy, the sensitive analysis of the protein was realized. Importantly, the cathode signal was enhanced significantly to improve the detection sensitivity and extend the detection range of the protein, providing a new perspective for the application in real biological samples and clinical diagnosis.

Section snippets

Synthesis of P3HT-PbS nanocomposites

The P3HT-PbS nanocomposites were prepared by reprecipitation. Briefly, under vigorously stirring, 0.2 mg P3HT was dissolved in 0.6 mL CHCl3 to acquire a homogeneous solution. Simultaneously, 4.0 mmol/L Pb(NO3)2 aqueous solution was added by 20 μL TGA, followed by adjusting pH value to 11 and then continuously purging pure nitrogen to eliminate oxygen. Subsequently, the obtained Pb(NO3)2 solution was injected into above mentioned P3HT homogeneous solution under rapid agitation. After the

Morphology and component characterization for nanoparticles

Herein, the SEM was employed to give an intuitive morphology description of prepared nanocomposites. As illustrated in Fig. 1A, the synthetic P3HT microcrystals exhibited well-distributed regular cube structure with a boundary length of 150 nm. Moreover, as shown in Fig. 1B, p-typed PbS quantum dot presented a round dot of about 10 nm in diameter. After the modification of PbS quantum dot on P3HT microcrystals surface to form P3HT-PbS nanocomposites, we could clearly see the monodisperse rough

Conclusion

In summary, a sensitive cathode PEC biosensor for detection of β2-MG was established. First, the organic-inorganic hybrid nanocomposite P3HT-PbS was synthesized as substrate to obtain an initial cathode photocurrent signal. Target related RCA reaction was introduced to form substantial G-quadruplexes structure for loading massive hemin. The formed hemin/G-quadruplexes could accept the illuminated electron, causing the conversion of Fe(III)/Fe(II) in hemin and thus reducing charge recombination

CRediT authorship contribution statement

Han-Mei Deng: Conceptualization, Data curation, Formal analysis, Investigation, Writing – original draft, Writing – review & editing. Ming-Jun Xiao: Data curation, Investigation. Ya-Qin Chai: Funding acquisition, Resources, Project administration, Supervision. Ruo Yuan: Funding acquisition, Resources, Project administration, Supervision. Ya-Li Yuan: Funding acquisition, Resources, Writing – review & editing.

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.

Acknowledgments

This work was supported by the Fundamental Research Funds for the Central University (XDJK2020TY002, XDJK2019B022), the National Natural Science Foundation of China (NNSF) of China (22176153, 22174113).

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