Tailoring the Superatomic Characteristics and Optical Behavior of Metal-Free Boron Clusters via Ligand Engineering.

It is of great importance to understand how the number and type of ligands influence the properties of clusters through ligand engineering, as this knowledge is crucial for the rational design and optimization of functional materials. Herein, the geometrical structures, binding energies, and electronic properties of nonmetallic Bn (n = 20 and 40) clusters with CO, PEt3, F, NO2, and CN ligands are systematically explored based on density functional theory (DFT) calculations. Our findings demonstrate that the CO ligand acts as an electron donor when attached to these two boron clusters, in contrast to their role as electron acceptors in interactions with metal oxide and metal chalcogenide clusters. This emphasizes the necessity of considering the intrinsic properties of the host cluster when modifying with ligands. Moreover, it was observed that substituting PEt3 with F, NO2, or CN converted the B20 cluster from an electron acceptor to an electron donor, thereby demonstrating the versatility in tuning the redox characteristics of boron clusters by selecting appropriate ligands. Intriguingly, the attachment of the PEt3, F, NO2, and CN ligands to B20 can significantly modulate the electronic properties of B20 to realize the formation of metal-free superalkali (B20(PEt3)n, n = 3-5) and superhalogen (B20F, B20NO2, and B20CN) clusters. Furthermore, the structure, stability, and optical absorption of the charge transfer complex B20(PEt3)3+B20F were analyzed. This complex has been identified as an efficient material for harvesting visible light. Our findings provide insights into the effects of ligand variations on boron cluster functionalities, offering a new perspective for the design of advanced materials with tailored cluster properties through ligand engineering.

Unraveling the Solvent Regulation in the Heteroatom-Doped Endohedral Gold Clusters: A Theoretical Study on the Electronic Properties and O2 Activation.

Liquid-phase synthesis of atomically precise nanoclusters has experienced rapid development recently, where polar solvents are indispensable in such a process. However, the regulation effect of solvents on the structural and electronic properties of different metal clusters and cluster assembly materials is still not well understood. Herein, a comprehensive density functional theory calculation has been performed to explore the solvation effect on heteroatom-doped endohedral gold clusters that always have remarkable stabilities and tunable electronic structures. The solvation free energy of the M@Au12 clusters (M = Cr, Mo, W, Co, Rh, Ir, Cu, Ag, and Au) was found to be related to the charge distribution of the central doped-atom M and the outer Au12 cage. Moreover, the aqueous solvent was observed to be able to increase the adsorption capacity of M@Au12 to O2 following the activation of O2 through the charge transfer from M@Au12 to O2, in which the transferred electrons occupy the π antibonding orbital of O2. In addition, the water solvent can also improve the hydrogenation reaction of O2 to form OOH over M@Au12, where the activation energy barrier for this process is very low with the participation of the solvent. Considering the importance of solvents in the liquid-phase synthesis of atomically precise clusters, these findings highlighted here could provide valuable theoretical guidance in potential applications of functional gold nanoclusters, especially in the liquid-phase cluster catalysis.

Dual External Field Strategy in Regulating the Superhalogen Characteristics of the Non-Noble Metal Constituted Tantalum Oxide Clusters.

The identification of the non-noble metal constituted TaO cluster as a potential analogue to the noble metal Au is significant for the development of tailored materials. It leverages the superatom concept to engineer properties with precision. However, the impact of incrementally integrating TaO units on the electronic configurations and properties within larger TaO-based clusters remains to be elucidated. By employing the density functional theory calculations, the global minima and low-lying isomers of the TanOn (n = 2-5) clusters were determined, and their structural evolution was disclosed. In the cluster series, Ta5O5 was found to possess the highest electron affinity (EA) with a value of 2.14 eV, based on which a dual external field (DEF) strategy was applied to regulate the electronic property of the cluster. Initially, the electron-withdrawing CO ligand was affixed to Ta5O5, followed by the application of an oriented external electric field (OEEF). The CO ligation was found to be able to enhance the Ta5O5 cluster's electron capture capability by adjusting its electron energy levels, with the EA of Ta5O5(CO)4 peaking at 2.58 eV. Subsequently, the introduction of OEEF further elevated the EA of the CO-ligated cluster. Notably, OEEF, when applied along the +x axis, was observed to sharply increase the EA to 3.26 eV, meeting the criteria for superhalogens. The enhancement of EA in response to OEEF intensity can be quantified as a functional relationship. This finding highlights the advantage of OEEF over conventional methods, demonstrating its capacity for precise and continuous modulation of cluster EAs. Consequently, this research has adeptly transformed tantalum oxide clusters into superhalogen structures, underscoring the effectiveness of the DEF strategy in augmenting cluster EAs and its promise as a viable tool for the creation of superhalogens.

Electric Field Promoted Click Surface-Enhanced Raman Spectroscopy for Rapid and Specific Detection of DNA 2-Deoxyribose 5'-Aldehyde Oxidation Products in Plasma.

Rapid identification of DNA oxidative damage sites is of great significance for disease diagnosis. In this work, electric field-regulated click reaction surface-enhanced Raman spectroscopy (e-Click-SERS) was developed aiming at the rapid and specific analysis of furfural, the biomarker of oxidative damage to the 5-carbon site of DNA deoxyribose. In e-Click-SERS, cysteamine-modified porous Ag filaments (cys@p-Ag) were prepared and used as electrodes, amine-aldehyde click reaction sites, and SERS substrates. Cysteamine was controlled as an "end-on" conformation by setting the voltage of cys@p-Ag at -0.1 V, which ensures its activity in participating in the amine-aldehyde click reaction during the detection of furfural. Benefiting from this, the proposed e-Click-SERS method was found to be sensitive, rapid-responding, and interference-resistant in analyzing furfural from plasma. The method detection limits of furfural were 5 ng mL-1 in plasma, and the whole "extraction and detection" procedure was completed within 30 min with satisfactory recovery. Interference from 13 kinds of common plasma metabolites was investigated and found to not interfere with the analysis, according to the exclusive adaptation of the amine-aldehyde click reaction. Notably, the e-Click-SERS technique allows in situ analysis of biological samples, which offers great potential to be a point-of-care testing tool for detecting DNA oxidative damage.

Dynamic SPME-SERS Induced by Electric Field: Toward In Situ Monitoring of Pharmaceuticals and Personal Care Products.

The core of the surface-enhanced Raman spectroscopy (SERS)-based techniques for dynamic monitoring is to realize rapid and reversible adsorption. Herein, the integration technology of electro-enhanced adsorption, solid-phase microextraction, and surface-enhanced Raman spectroscopy (EE-SPME-SERS) was developed to obtain sensitive, ultrafast, and reversible SERS response toward in situ monitoring of pharmaceuticals and personal care products (PPCPs). In the EE-SPME-SERS method, a roughened Ag fiber with Au modification (r-Ag/Au fiber) was used as the SERS substrate, SPME sorbent, and working electrode. The r-Ag/Au fiber displayed good SERS sensitivity, ultrahigh photostability, and adsorption properties. The adsorption efficiency of benzidine was 76 times accelerated in EE-SPME-SERS compared to that in static adsorption. The whole process of "sampling and detection" in EE-SPME-SERS can be finished within 1 s. Reversible adsorption and desorption can be achieved in situ by switching the direction of electric field, and the regeneration process takes only a few minutes. Simulated release of benzidine from household wastewater was in situ and dynamically monitored using this strategy. EE-SPME-SERS was proved universal for ionized PPCPs and can detect multicomponents simultaneously. In addition, EE-SPME-SERS showed very good analytical properties. Great potential of EE-SPME-SERS can be expected in environmental monitoring.

On the Precise and Continuous Regulation of the Superatomic and Spectroscopic Behaviors of the Quasi-Cubic W4C4 Cluster by the Oriented External Electric Field.

Designing and realizing novel superatoms with controllable and tunable electronic properties is vital for their potential applications in cluster-assembly nanomaterials. Here, we investigated the effect of the oriented external electric field (OEEF) on the geometric and electronic structures as well as the spectroscopic properties of the quasi-cubic W4C4 cluster by utilizing the density functional theory (DFT) calculations. Compared with traditional models, the OEEF was observed to hold the special capability in continuously and precisely modulating the electronic properties of W4C4, that is, remarkably increasing its electron affinity (EA) (1.58 eV) to 5.61 eV under the 0.040 au OEEF (larger than any halogen atoms in the periodic table), which possesses the superhalogen behavior. Furthermore, the downward movement of the lowest unoccupied molecular orbital level of the cluster accompanied by the enhancement of the OEEF intensity was demonstrated to be the origin of the EA increment. Additionally, the photoelectron spectra (PES) of W4C4- were also simulated under different OEEF intensities, where the PES peaks move to a higher energy area following the enhancement of the OEEF strength, exhibiting the blue-shift behavior. These findings observed here open a new avenue in conveniently and precisely adjusting the electronic properties of clusters, which will be beneficial for the rational design of superatoms or superatom-assembled nanomaterials under the external field.

A Three-Dimensional Conductive Scaffold Microchip for Effective Capture and Recovery of Circulating Tumor Cells with High Purity.

Effective acquirement of highly pure circulating tumor cells (CTCs) is very important for CTC-related research. However, it is a great challenge since abundant white blood cells (WBCs) are always co-collected with CTCs because of nonspecific bonding or low depletion rate of WBCs in various CTC isolation platforms. Herein, we designed a three-dimensional (3D) conductive scaffold microchip for highly effective capture and electrochemical release of CTCs with high purity. The conductive 3D scaffold was prepared by dense immobilization of gold nanotubes (Au NTs) on porous polydimethylsiloxane and was functionalized with a CTC-specific biomolecule facilitated by a Au-S bond before embedding into a microfluidic device. The spatially distributed 3D macroporous structure compelled cells to change migration from linear to chaotic and the densely covered Au NTs enhanced the topographic interaction between cells and the substrate, thus synergistically improving the CTC capture efficiency. The Au NT-coated 3D scaffold had good electrical conductivity and the Au-S bond was breakable by voltage exposure so that captured CTCs could be specifically released by electrochemical stimulation while nonspecifically bonded WBCs were not responsive to this process, facilitating recovery of CTCs with high purity. The 3D conductive scaffold microchip was successfully applied to obtain highly pure CTCs from cancer patients' blood, benefiting the downstream analysis of CTCs.

Flexible Three-Dimensional Net for Intravascular Fishing of Circulating Tumor Cells.

Current strategies for in vitro isolation of circulating tumor cells (CTCs) fail to detect extremely rare CTCs heterogeneously distributed in blood. It is possible to devise methods for in vivo capture of CTCs based on processing almost all of the blood in the human body to improve detection sensitivity, but the complicated manipulation, biosafety concerns, and limited capture efficiency of conventional detection strategies prohibit their implementation in the clinic. Herein, we present a flexible three-dimensional (3-D) CTC-Net probe for intravascular collection of CTCs. The CTC-Net, consisting of a 3-D elastic scaffold with an interconnected, spatially distributed network accommodates a large quantity of immobilized antibodies and provides an enhanced substrate-cell contact frequency, which results in an enhanced capture efficiency and effective detection of heterogeneous CTCs. The as-prepared CTC-Net can be readily compressed and injected into blood vessels and fully unfolded to form a 3-D "fishing-net" structure for capture of the CTCs, and then retracted for imaging and downstream gene analysis of the captured CTCs. Significant advantages for the CTC-Net over currently available in vitro and in vivo procedures are demonstrated for detection of extremely rare CTCs from wild-type rats and successful capture of CTCs and CTC clusters before metastasis in the case of tumor-bearing rats. Our research demonstrates for the first time the use of a 3-D scaffold CTC-Net probe for in vivo capture of CTCs. The method shows exceptional performance for cell capture, which is readily implemented and holds great potential in the clinic for early diagnosis of cancer.

Caramelized carbonaceous shell-coated γ-Fe2O3 as a magnetic solid-phase extraction sorbent for LC-MS/MS analysis of triphenylmethane dyes.

Carbonaceous shell-coated γ-Fe2O3 nanoparticles (γ-Fe2O3@CNM) were synthesized from glucose caramelization and used as a novel magnetic solid-phase extraction medium for malachite green and crystal violet in environmental water. Malachite green and crystal violet were absorbed on to γ-Fe2O3@CNM by electrostatic and π-interactions. The morphologies, pore structures, surface functional groups, and magnetic properties of γ-Fe2O3@CNM were characterized by TEM, FTIR, hysteresis regression, Brunauer-Emmet-Teller analysis, zeta potential, XPS, and XRD. The magnetic solid-phase extraction procedure was optimized by extraction pH, absorption time, desorption solvent, and desorption time. The absorption capacities (qmax values) for malachite green and crystal violet were 34.2 and 27.9 mg g-1, respectively. After magnetic solid-phase extraction, malachite green and crystal violet were determined by LC-MS/MS. The analytical method was validated with a linear range of 0.02-20 ng mL-1, enrichment factor of 25.8 and 25.4, method detection limit of 0.004 ng mL-1, and intra-day precisions of 2.1% and 2.6% for malachite green and crystal violet, respectively. The relative recovery was found to be 73.4-101.5% for malachite green and 83.1-102.7% for crystal violet upon the application of the magnetic solid-phase extraction method to real water samples from lake, spring, sea, fishpond, and industrial waste. Graphical abstract Caramelized-carbon-coated magnetic nanoparticles are used as novel extraction medium based on electrostatic and π-interactions. It is porous, amphiphilic, electronegative, magnetically strong, and features abundant absorption site. These characteristics stimulate mass transfer and result in a useful MSPE method in environmental analysis.

Unveiling the electronic structures and ligation effect of the superatom-polymeric zirconium oxide clusters: a computational study.

Discovering the non-noble ZrO cluster as an analog of the noble metal catalyst Pd is of significance toward designing functional materials with fine-tuned properties using the superatom concept. The effect of gradually assembling the ZrO superatomic unit on the electronic structures and chemical bonding of larger ZrO-polymeric clusters, however, is unclear. Herein, by using density functional theory (DFT) calculations, the lowest-energy structures and low-lying isomers of the (ZrO)n-/0 (n = 2-5) clusters were optimized, in which every O atom in these clusters tends to connect its adjacent two Zr atoms forming metal oxygen bridge bonds. Insights into the electronic characteristics of these clusters were obtained by analyzing their molecular orbitals (MOs) and density of states (DOS). More importantly, our studies on the CO (electron acceptor) and PH3 (electron donor) ligated Zr3O3 clusters unveil that the ligation process can substantially alter the electronic properties of the clusters by tuning the HOMO and LUMO states, which may have potential applications in photovoltaics. Strikingly, the successive attachment of PH3 on Zr3O3 dramatically lowers the adiabatic ionization potential (AIP) of the ligated clusters, resulting in the formation of stable superalkali clusters with large HOMO-LUMO gaps. Furthermore, the potential of constructing the superalkali Zr3O3(PH3)5 based 1-D cluster assembled material was also examined.

Flexible Electrochemical Urea Sensor Based on Surface Molecularly Imprinted Nanotubes for Detection of Human Sweat.

Flexible electrochemical (EC) sensors have shown great prospect in epidermal detection for personal healthcare and disease diagnosis. However, no reports have been seen in flexible device for urea analysis in body fluids. Herein, we developed a flexible wearable EC sensor based on surface molecularly imprinted nanotubes for noninvasive urea monitoring with high selectivity in human sweat. The flexible EC sensor was prepared by electropolymerization of 3,4-ethylenedioxythiophene (EDOT) monomer on the hierarchical network of carbon nanotubes (CNTs) and gold nanotubes (Au NTs) to imprint template molecule urea. This sensor exhibited a good linear response toward physiologically relevant urea levels with negligible interferences from common coexisting species. Bending test revealed that this sensor possessed excellent mechanical tolerance and its EC performance was almost not affected by bending deformation. On-body results of human subjects showed that the flexible platform could distinctly respond to the urea levels in volunteer's sweat after aerobic exercise. The new flexible epidermal EC sensor can provide useful insights into noninvasive monitoring of urea levels in various biofluids, which is promising in the clinical diagnosis of diverse biomedical applications.

Construction of Highly Efficient Resonance Energy Transfer Platform Inside a Nanosphere for Ultrasensitive Electrochemiluminescence Detection.

Electrochemiluminescence (ECL) detection has attracted increasing attention as a promising analytical approach. A considerable number of studies showed that ECL intensity can be definitely improved by resonance energy transfer (RET), while the RET efficiency is strongly dependent on the distance between exited donors and acceptors. Herein we disclose for the first time a highly enhanced RET strategy to promote the energy transfer efficiency by coencapsulating the donor ([Ru(bpy)3]2+)/acceptor (CdTe quantum dots, CdTe QDs) pairs into a silica nanosphere. Plenty of [Ru(bpy)3]2+ and CdTe QDs closely packed inside a single nanosphere greatly shortens the electron-transfer path and increases the RET probability, therefore significantly enhancing the luminous efficiency. Further combining with molecularly imprinting technique, we develop a novel ECL sensor for ultrasensitive and highly selective detection of target molecules. Proof of concept experiments showed that extremely low detection limits of subfg/mL (S/N = 3) with broad linear ranges (fg/mL to ng/mL) could be obtained for detection of two kinds of mycotoxins (α-ergocryptine and ochratoxin A) that are recognized as potential health hazards at very low concentrations. This strategy combining enhanced RET system and molecularly imprinting technique, represents a versatile ECL platform toward low-cost, rapid, ultrasensitive, and highly selective detection of target molecules in diverse applications.

Probing the Geometric and Electronic Structures of the Monogadolinium Oxide GdO n-1/0 ( n = 1-4) Clusters.

The existence of abundant 4f electrons significantly increases the complexity and difficulty in precisely determining the geometric and electronic structures of the lanthanide oxide clusters. Herein, by combining the photoelectron imaging spectroscopy and density functional theory (DFT) calculations, the electronic structure of GdO was investigated. An electron affinity (EA) of 1.16 ± 0.09 eV is obtained, and the measured anisotropy parameter (ß) provides direct experimental evidence about the orbital symmetry of the detached electron in GdO-. DFT calculations have been employed to acquire the optimized geometries of the GdO n-1/0 ( n = 2-4) clusters, and multiple activated oxygen species, which are radical, peroxide, superoxide, triradical, and ozonide radical, are found in these oxide clusters. Simulated photoelectron spectra (PES) of the GdO n-1/0 ( n = 2-4) clusters are examined, which may stimulate further experimental investigations on the gadolinium oxide clusters. In addition, the valence molecular orbitals (MOs) of these clusters are also discussed to reveal the interaction between the lanthanide metal (Gd) and O atoms.

Mimicking the magnetic properties of rare earth elements using superatoms.

Rare earth elements (REs) consist of a very important group in the periodic table that is vital to many modern technologies. The mining process, however, is extremely damaging to the environment, making them low yield and very expensive. Therefore, mimicking the properties of REs in a superatom framework is especially valuable but at the same time, technically challenging and requiring advanced concepts about manipulating properties of atom/molecular complexes. Herein, by using photoelectron imaging spectroscopy, we provide original idea and direct experimental evidence that chosen boron-doped clusters could mimic the magnetic characteristics of REs. Specifically, the neutral LaB and NdB clusters are found to have similar unpaired electrons and magnetic moments as their isovalent REs (namely Nd and Eu, respectively), opening up the great possibility in accomplishing rare earth mimicry. Extension of the superatom concept into the rare earth group not only further shows the power and advance of this concept but also, will stimulate more efforts to explore new superatomic clusters to mimic the chemistry of these heavy atoms, which will be of great importance in designing novel building blocks in the application of cluster-assembled nanomaterials. Additionally, based on these experimental findings, a novel "magic boron" counting rule is proposed to estimate the numbers of unpaired electrons in diatomic LnB clusters.

Three-Dimensional Scaffold Chip with Thermosensitive Coating for Capture and Reversible Release of Individual and Cluster of Circulating Tumor Cells.

Tumor metastasis is attributed to circulating tumor cells (CTC) or CTC clusters. Many strategies have hitherto been designed to isolate CTCs, but there are few methods that can capture and gently release CTC clusters as efficient as single CTCs. Herein, we developed a three-dimensional (3D) scaffold chip with thermosensitive coating for high-efficiency capture and release of individual and cluster CTCs. The 3D scaffold chip successfully combines the specific recognition and physically obstructed effect of 3D scaffold structure to significantly improve cell clusters capture efficiency. Thermosensitive gelatin hydrogel uniformly coated on the scaffold dissolves at 37 °C quickly, and the captured cells are gently released from chip with high viability. Notably, this platform was applied to isolate CTCs from cancer patients' blood samples. This allows global DNA and RNA methylation analysis of collected single CTC and CTC clusters, indicating the great potential of this platform in cancer diagnosis and downstream analysis at the molecular level.

High-Efficiency Capture of Individual and Cluster of Circulating Tumor Cells by a Microchip Embedded with Three-Dimensional Poly(dimethylsiloxane) Scaffold.

Effective isolation of circulating tumor cells (CTCs) has great significance for cancer research but is highly challenged. Here, we developed a microchip embedded with a three-dimensional (3D) PDMS scaffold by a quadratic-sacrificing template method for high-efficiency capture of CTCs. The microchip was gifted with a 3D interconnected macroporous structure, strong toughness, and excellent flexibility and transparency, enabling fast isolation and convenient observation of CTCs. Especially, 3D scaffold chip perfectly integrates the two main strategies currently used for enhancement of cell capture efficiency. Spatially distributed 3D scaffold compels cells undergoing chaotic or vortex migration in the channel, and the spatially distributed nanorough skeleton offers ample binding sites, which synergistically and significantly improve CTCs capture efficiency. Our results showed that 1-118 CTCs/mL were identified from 14 cancer patients' blood and 5 out of these cancer patients showed 1-14 CTC clusters/mL. This work demonstrates for the first time the development of microchip with transparent interconnected 3D scaffold for isolation of CTCs and CTC clusters, which may promote in-depth analysis of CTCs.

Photoelectron imaging spectroscopy of niobium mononitride anion NbN(.).

In this gas-phase photoelectron spectroscopy study, we present the electron binding energy spectrum and photoelectron angular distributions of NbN(-) by the velocity-map imaging technique. The electron binding energy of NbN(-) is measured to be 1.42 ± 0.02 eV from the X band maximum which defines the 0-0 transition between ground states of anion and neutral. Theoretical binding energies which are the vertical and adiabatic detachment energies are computed by density functional theory to compare them with experiment. The ground state of NbN(-) is assigned to the (2)Δ3/2 state and then the electronic transitions originating from this state into X(3)ΔΩ (Ω = 1-3), a(1)Δ2, A(3)Σ1 (-), and b(1)Σ0 (+) states of NbN are reported to interpret the spectral features. As a prospective study for catalytic materials, spectral features of NbN(-) are compared with those of isovalent ZrO(-) and Pd(-).

S-P coupling induced unusual open-shell metal clusters.

Metal clusters featuring closed supershells or aromatic character usually exhibit remarkably enhanced stability in their cluster series. However, not all stable clusters are subject to these fundamental constraints. Here, by employing photoelectron imaging spectroscopy and ab initio calculations, we present experimental and theoretical evidence on the existence of unexpectedly stable open-shell clusters, which are more stable than their closed-shell and aromatic counterparts. The stabilization of these open-shell Al-Mg clusters is proposed to originate from the S-P molecular orbital coupling, leading to highly stable species with increased HOMO-LUMO gaps, akin to s-p hybridization in an organic carbon atom that is beneficial to form stable species. Introduction of the coupling effect highlighted here not only shows the limitations of the conventional closed-shell model and aromaticity but also provides the possibility to design valuable building blocks.

Engineered decomposable multifunctional nanobioprobes for capture and release of rare cancer cells.

Early detection and isolation of circulating tumor cells (CTCs) can provide helpful information for diagnosis, and functional readouts of CTCs can give deep insight into tumor biology. In this work, we presented a new strategy for simple isolation and release of CTCs using engineered nanobioprobes. The nanobioprobes were constructed by Ca(2+)-assisted layer-by-layer assembly of alginate onto the surface of fluorescent-magnetic nanospheres, followed by immobilization of biotin-labeled anti-EpCAM. As-prepared anti-EpCAM-functionalized nanobioprobes were characterized with integrated features of anti-EpCAM-directed specific recognition, fluorescent magnetic-driven cell capture, and EDTA-assisted cell release, which can specifically recognize 10(2) SK-BR-3 cells spiked in 1 mL of lysed blood or human whole blood samples with 89% and 86% capture efficiency, respectively. Our proof-of-concept experiments demonstrated that 65% of captured SK-BR-3 cells were released after EDTA treatment, and nearly 70% of released SK-BR-3 cells kept their viability, which may facilitate molecular profiling and functional readouts of CTCs.

Observation of d-p hybridized aromaticity in lanthanum-doped boron clusters.

The concept of aromaticity has been advanced beyond the framework of organic chemistry, and multiple aromaticity (σ, π, and δ) has been observed to account for the highly symmetric structures or unusual stability of the clusters. In the present study, the electronic structures and chemical bonding of small monolanthanum boride clusters are investigated using photoelectron imaging spectroscopy and first principles electronic structure calculations. Accurate electron affinities of 1.32 ± 0.04 and 1.13 ± 0.06 eV for the neutral LaB2 and LaB3 clusters are obtained by the vibrationally-resolved photoelectron spectra of the LaB2(-) and LaB3(-) clusters, respectively. It is shown that LaB2(-) and LaB3 exhibit enhanced stability in their respective cluster series, as evidenced from the calculated removal energies and HOMO-LUMO gaps. Molecular orbital analysis discloses that these two clusters possess doubly aromatic characters (σ and π), responsible for their enhanced stability. Interestingly, unlike conventional σ-, π-, and δ-aromaticity formed by the delocalization of unhybridized p or d orbitals, the σ and π delocalized molecular orbitals shown here are formed through the effective overlap between the 5d atomic orbital of the La atom and the p orbitals of the remaining boron atoms, representing an intriguing d-p hybridized aromaticity.