Quantum dot imaging in the second near-infrared optical window: studies on reflectance fluorescence imaging depths by effective fluence rate and multiple image acquisition

Abstract

Quantum dot (QD) imaging capability was investigated by the imaging depth at a near-infrared second optical window (SOW; 1000 to 1400 nm) using time-modulated pulsed laser excitations to control the effective fluence rate. Various media, such as liquid phantoms, tissues, and in vivo small animals, were used and the imaging depths were compared with our predicted values. The QD imaging depth under excitation of continuous 20 mW/cm(2) laser was determined to be 10.3 mm for 2 wt%hemoglobin phantom medium and 5.85 mm for 1 wt% intralipid phantom, which were extended by more than two times on increasing the effective fluence rate to 2000 mW/cm(2). Bovine liver and porcine skin tissues also showed similar enhancement in the contrast-to-noise ratio (CNR) values. A QD sample was inserted into the abdomen of a mouse.With a higher effective fluence rate, the CNR increased more than twofold and the QD sample became clearly visualized, which was completely undetectable under continuous excitation.Multiple acquisitions of QD images and averaging process pixel by pixel were performed to overcome the thermal noise issue of the detector in SOW, which yielded significant enhancement in the imaging capability, showing up to a 1.5 times increase in the CNR.

Biocompatible Semiconductor Quantum Dots as Cancer Imaging Agents

“…Short‐wave infrared light (1000–2000 nm) passes even more readily through biological tissue, but is inefficiently detected by traditional CCD cameras and will require the adoption of InGaAs detectors for optimal signal collection . However, using InGaAs detectors in combination with NIR II‐emitting QDs with high PL QY can potentially enable greater imaging depths (>2 cm) than can be achieved by conventional small molecule dyes in the NIR II range that suffer from low PL QY and poor stability …”

Colloidal Second Near‐Infrared‐Emitting Mn‐Doped Ag2S Quantum Dots

“…However, the emission wavelength of fluorescent probes has been encouraged to extend to near‐infrared range for acquiring enhanced light penetration into biological tissue, which facilitates the coordinated conjunction with MRI . The second near infrared (NIR−II, 1000–1700 nm) optical window can provide deep tissue penetration offering significantly extended imaging depths . In our previous study, the reduced scattering of NIR−II QD signals made the imaging depth in skin tissues three times deeper than QDs emitting at 800 nm which is at the conventional first near infrared (NIR−I, 650–950 nm) window under an equivalent imaging condition as for the NIR−II QDs .…”

“…[9] The second near infrared (NIRÀ II, 1000-1700 nm) optical window can provide deep tissue penetration offering significantly extended imaging depths. [10][11][12][13] In our previous study, the reduced scattering of NIRÀ II QD signals made the imaging depth in skin tissues three times deeper than QDs emitting at 800 nm which is at the conventional first near infrared (NIRÀ I, 650-950 nm) window under an equivalent imaging condition as for the NIRÀ II QDs. [12] Ag 2 S QDs can emit at NIRÀ II and are composed of less toxic elements than other NIRÀ II emitting QDs such as PbS, PbSe, InAs, Cd 3 As 2 , HgS, and HgSe, which offers great biocompatibility.…”

Cancer-Microenvironment-Sensitive Activatable Quantum Dot Probe in the Second Near-Infrared Window

“…A PA-NIRQD PBS buffer solution (1 μM) was evenly sprayed onto the entire colon tissue surface (see SI for details), and ex vivo NIR-II FL reflectance imaging was conducted at various time points using a home-built imaging system equipped with an InGaAs CCD camera . The colon tissues were excited by a time-modulated 910 nm pulse laser at a fluence rate of 200 mW/cm 2 . Four spots (T1–T4 in Figure b) were arbitrarily chosen at the tumor site, and a large area of normal mucosa (Box N in Figure b) was chosen as a control.…”

“…3 The colon tissues were excited by a time-modulated 910 nm pulse laser at a fluence rate of 200 mW/cm 2 . 38 Four spots (T1−T4 in Figure 5b) were arbitrarily chosen at the tumor site, and a large area of normal mucosa (Box N in Figure 5b) was chosen as a control. The FL intensities were recorded over time at the four tumor spots and the control area (Figure 5c); all four tumor spots showed rapid increases in FL ranging from 150% to 300% within 10 min, whereas the change in FL in area N was negligible.…”