A novel probe based on phenylboronic acid functionalized carbon nanotubes for ultrasensitive carbohydrate determination in biofluids and semi-solid biotissues

Abstract

Carbohydrates are known to be involved in a wide range of biological and pathological processes. However, due to the presence of multiple hydroxyl groups, carbohydrate recognition is a particular challenge. Herein, we reported an ultrasensitive solid-phase microextraction (SPME) probe based on phenylboronic acid (PBA) functionalized carbon nanotubes (CNTs) for direct in vitro or in vivo recognition of carbohydrates in biofluids as well as semi-solid biotissues. The coating of the proposed probe possessed a 3D interconnected porous architecture formed by the stacking of CNTs. As a result, the binding capacity toward carbohydrates was excellent. The proposed approach was demonstrated to be much superior to most carbohydrate sensors, including higher sensitivity, wider linear range, and excellent qualitative ability in multi-carbohydrate systems. Thus, this approach opens up new avenues for the facile and efficient recognition of carbohydrates for important applications such as glycomics.

Scheme 1. Representation of the carbohydrate recognition with the probe based on PBA functionalized-CNTs.

Fig. 1. High TEM image (A), IR spectra, (B) and entire XPS spectrum (C) of the synthesized PBA functionalized-CNTs; (D) the selectivity of PBA functionalized-CNTs toward cis-diol.

Fig. 2. TEM images of the surface (A) and cross section (B) of the PBA functionalized-CNTs probe; TEM images of the surface (C) and cross section (D) of the PBA functionalized-carbon dots probe. It could be observed that no 3D interconnected pores were formed in the PBA functionalized-carbon dots probe; (E) the proposed probe with nanotube stacking possessed higher binding capacities than that based on PBA functionalized-carbon dots (nanoparticle stack). Note: the two kinds of probes were prepared in the same way; (F) concentrations of glucose in eluent at different pH (exposure time: 40 min); (G) comparison of the binding capacities of the PBA functionalized-CNTs probe with other widely used probes and the non-PBA functionalized probe.

Fig. 3. The response of the probe toward various potential interfering substances. The mixture, which contained glucose, various amino acids, aliphatic acids, glutathione and uric acid (concentrations = 10 μM), was extracted by the probe for 40 min. The result showed that the probe presented specific selectivity towards carbohydrate (glucose). The inset shows the response of the probe toward glucose in the solution without and with interfering substances.

Fig. 4. (A) Binding kinetics of the proposed probe toward glucose in PBS solution (100 μM glucose); (B) the wide linear range of glucose in PBS solution.

Fig. 5. The linear ranges (A) and enrichment factors (B) of multi-carbohydrates in PBS solution using the proposed probe.

Fig. 6. (A) The in vivo sampling procedure in plant tissues. The carbohydrate probe is deployed under the guidance of a steel needle (a), removal of the steel needle and exposure of the probe to the carbohydrate in plant tissues (b), the steel needle is carefully put back in the plant tissue at the end of sampling (C), the carbohydrate probe is removed (d). The probe was readily inserted into or removed from plant tissues; (B) biological macromolecules analysis in the eluent with MALDI-TOF MS; (C) carbohydrate assay in the stem of Malabar spinach and leaf of aloe. The signals of the corresponding carbohydrate were apparent; (D) in vivo continuous carbohydrate monitoring in aloe leaf using the proposed probe.