Recent research progress of selenotungstate-based biomolecular sensing materials.

Polyoxometalates (POMs) have drawn significant attention on account of their structural designability, compositional diversity and great potential applications. As an indispensable branch of POMs, selenotungstates (SeTs) have been synthesized extensively. Some SeTs have been applied as sensing materials for detecting biomarkers (e.g., metabolites, hormones, cancer markers). To gain a comprehensive understanding of advancements in SeT-based sensing materials, we present an overview that encapsulates the sensing performances and mechanisms of SeT-based biosensors. SeT-based biosensors are categorized into electrochemical catalytic biosensors, electrochemical affinity biosensors, "turn-off" fluorescence biosensors and "turn-on" fluorescence biosensors. We anticipate the expansive potential of SeT-based biosensors in wearable and implantable sensing technologies, which promises to catalyze significant breakthroughs in SeT-based biosensors.

2,5-Thiophenedicarboxylic Acid Bridging Hexameric CeIII-Substituted Selenotungstate and Its Application for Detecting Mucin 1.

The development of polyoxometalate chemistry not only is derived from the continuous discovery of novel polyoxometalates (POMs) but also stems from the exploitation of their new functionalities. In this work, we obtained a rigid sulfur-containing heterocyclic ligand-linking aggregate [N(CH3)4]10Na6H6[Ce8(H2O)26W8(HTDA)2(TDA)2O20][SeW4O18]2[SeW9O33]4·112H2O (1) (H2TDA = 2,5-thiophenedicarboxylic acid). Its polyanionic unit consists of one [Ce4(H2O)13W4O10(HTDA)(TDA)O10]18+ cluster and two kinds of Keggin-type [SeW4O18] and [SeW9O33] segments. It is noteworthy that H2TDA ligands not only work as connectors to link two symmetrical {[Ce4(H2O)13W4(HTDA)(TDA)O10][SeW4O18][SeW9O33]2}11- units but also function as ornaments to graft to the polyanionic backbone. Furthermore, 1 and 3,4-ethylenedioxythiophene (EDOT) were deposited on the glassy carbon electrode (GCE) by the electropolymerization (EPM) method, resulting in a 1-poly(3,4-ethylenedioxythiophene) (1-PEDOT) composite film, which can provide sufficient binding sites to immobilize Au nanoparticles (Au NPs). Hereafter, the Au NPs-immobilized 1-PEDOT modified electrode (Au/1-PEDOT/GCE) was used to construct an electrochemical aptasensor to detect mucin 1, showing a low detection limit of 29.5 fM in the Tris solution. This work not only demonstrates that rigid heterocyclic ligands are beneficial for the creation of novel rare-earth-substituted selenotungstate hybrids but also provides more enlightenment for POM-based materials used for electrochemical detection of cancer markers.

Multi-CeIII-Inserted Phospho(III)tungstate Containing Three Building Units with Prominent Peroxidase-Mimicking Activity for Detecting l-Cysteine.

An attractive isonicotinic acid-ornamented octa-CeIII-inserted phospho(III)tungstate [H2N(CH3)2]6Na8[Ce8(H2O)30W8Na2O20(INA)4][HPIIIW4O17]2[HPIIIW9O33]4·30H2O (1-Ce) (HINA = isonicotinic acid) has been isolated through the deliberately designed one-step assembly strategy, in which the HPO32- heteroanion template was introduced into the Ce3+/WO42- system in the presence of HINA. The polyoxoanion of 1-Ce consists of two identical [Ce4(H2O)15W4NaO10(INA)2][HPIIIW4O17][HPIIIW9O33]2}7- subunits linked by Ce-O-W bonds. The polyoxoanion exhibits three kinds of polyoxotungstate building blocks [W4NaO20(INA)2]17-, [HPIIIW4O17]6-, and [HPIIIW9O33]8-, in which [W4NaO20(INA)2]17- and [HPIIIW4O17]6- building units can be considered as seeds driven by the coordination of additional Ce3+ ions to induce aggregation of [HPIIIW9O33]8- fragments. Furthermore, 1-Ce possesses high peroxidase-like activity and can oxidize 3,3',5,5'-tetramethylbenzidine in the presence of H2O2 with a turnover rate of 6.20 × 10-3 s-1. Because l-cysteine (l-Cys) can reduce oxTMB to TMB, the detection of l-Cys was established based on the 1-Ce-based H2O2 colorimetric biosensing platform with the linear range of 5-100 µM and the limit of detection of 4.28 µM. This work not only can expand the scientific research studies on coordination chemistry and materials chemistry of rare-earth-inserted polyoxotungstates but also can provide practical application possibility in clinical diagnosis using liquid biopsy.

Lamellar Nanocomposite Based on a 1D Crayfish-like CeIII-Substituted Phospho(III)tungstate Semiconductor and Polyaniline Used as a High-Performance Humidity Sensing Device.

In order to meet people's demand for intelligent management of daily life and health, manufacturing and developing humidity monitoring equipment with convenience, high sensitivity, easy miniaturization, and low cost is particularly important in the era of rapid development of artificial intelligence and the Internet of Things. Polyaniline (PANI) is an attractive humidity sensing material due to its designable functional properties. However, PANI modified polyoxometalates (POMs) for humidity sensing are still rare. As a proof of concept, a novel moisture sensing composite material was obtained based on PANI and a novel 1D rare-earth-substituted phospho(III)tungstate [H2N(CH3)2]9Na3H6[Ce2(H2O)3W5O13(C2O4)][HPIIIW9O33]2[(HPIII)2W15O54]·42H2O (1). Notably, the anion structure of 1 contains trivacant Keggin-type [B-α-HPIIIW9O33]8- and Dawson-like [(HPIII)2W15O54]10- subunits linked by a heterometallic [Ce2(H2O)3W5O32(C2O4)]30- cluster. Furthermore, the 1/PANI composite shows a typical semiconductive characteristic with a "band-like" conductive mechanism. The fabricated 1/PANI-based humidity sensing device exhibits a broad sensing range (11∼97% relative humidity), fast response/recovery time (3.45 s/3.24 s), good repeatability, and long-term stability (over 3 months). Additionally, the possible sensing mechanism is proposed. This work offers an enormous possibility for the design of high-performance humidity sensing materials through POM material chemistry.

3-D Antimonotungstate Framework Based on 2,6-H2pdca-connecting Iron-Cerium Heterometallic Krebs-type Polyoxotungstates for Detecting Small Biomolecules.

An inorganic-organic hybrid 3-D FeIII-CeIII heterometallic antimonotungstate framework [Ce(H2O)5(2,6-pdca)]4H2[Fe4(H2O)6(SbW9O33)2]·38H2O (1) (2,6-H2pdca = 2,6-pyridine-dicarboxylic acid) has been synthesized via a hydrothermal method by the one-pot reaction of 2,6-H2pdca, FeCl3·6H2O, Ce(NO3)3·6H2O, and Na9[B-α-SbW9O33]·19.5H2O. Notably, the structural unit of 1 possesses a Krebs-type [Fe4(H2O)6(2,6-pdca)2(SbW9O33)2]10- subunit supported with four bridging [Ce(H2O)5(2,6-pdca)]+ moieties. It is worth highlighting that adjacent structural units are concatenated together through heterobimetallic bridges to construct a 3-D framework. Furthermore, cuboid nanocrystal 1' was prepared under mild hydrothermal conditions based on the electrostatic interaction between 1 and K+. The effects of concentration and time on the morphology of nanocrystal 1' were also studied. The cuboid nanocrystal 1' was used as a modified electrode material for simultaneous electrochemical detection of dopamine and acetaminophen. The 1'-modified glassy carbon electrode shows good selectivity and sensitivity for detecting dopamine and acetaminophen.

An unprecedented polyhydroxycarboxylic acid ligand bridged multi-EuIII incorporated tellurotungstate and its luminescence properties.

The first polyhydroxycarboxylic acid ligand bridged multi-EuIII-incorporated tellurotungstate K14H10[Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]·60H2O (H6glu = d-gluconic acid) (1) was synthesized via an organic ligand-driven self-assembly strategy. The polyhydroxycarboxylic acid ligand bridged tetrameric polyoxoanion [Eu4(H2O)4W6(H2glu)4O12(B-α-TeW9O33)4]24- in 1 can be viewed as an aggregation of four trivacant Keggin [B-α-TeW9O33]8- fragments and an innovative heterometallic [Eu4(H2O)4W6(H2glu)4O12]8+ cluster, in which four high-coordinate polyhydroxy flexible H2glu4- ligands chelate W and Eu centers through carboxyl and hydroxyl groups, giving rise to a heterometallic cluster. The hexagonal packing of the tetrameric polyoxoanions in 1 along the c axis provides excellent porous channels, which greatly increases the specific surface area of the whole framework and may be of benefit for fluorescence sensing in aqueous solution. 1 can function as a "turn-off" luminescence sensor to detect Cu2+ ions in aqueous solution. The limit of detection (LOD) of the 1-sensor is 8.82 × 10-6 mM, which is the lowest among the reported polyoxometalate-based fluorescence sensors. As for the Cu2+-quenching system, it can function as an "off-on" sensor to detect cysteine in an aqueous system, affording a LOD of 1.75 × 10-4 mM. This work opens up an avenue to broaden the applications of polyoxometalate-based materials in the optical intelligence detection field.